Take Five (cover)

The Bird

Sixty years ago today, I penned this entry in my then-diary:

Since yesterday I've been writing short poems - pretty good ones - if I do say so myself. It's usually about a person. One I especially like is:

Brother Adrian

When the boys go out to play,
Brother Adrian stayed away.
"Have to study," he just said,
"By tonight I will have read
Books of every type and kind,
For I simply have to find
How in French to write the words,
'Reading books is for the birds!'"

A little context: I was at that time in grade ten at De La Salle College "Oaklands" which was run by Christian Brothers, a Catholic teaching order. Brother Adrian was our then-new-to-us (two weeks prior) French teacher. When I read this doggerel a couple of days ago it brought to mind a Brother who had been nicknamed "the bird" by his students, based supposedly, as suggested by my friend Alfy who also went to De La Salle back then, on his behaviour. Now, neither Alfy nor I have a direct recollection (sixty years can do that) of the bird's identity but it makes sense to me that it might have been Brother Adrian, inspiring the poem's raison d'être by way of its terminal double entendre.

That would indeed have been clever but a little subsequent research suggests that "the bird" was actually Brother Michael (O'Reilly), not to be confused with Brother Michael (Dillon) [the former "junior", the latter, "senior"]. It appears that Michael O'Reilly's three-month stay (5 Sep 1966 - 5 Dec 1966, our home room teacher for the start of grade eleven) was scrubbed from his RIP assignment list. No wonder. We were the class from hell!

Janice, the jumping spider

The world

A random 5000-digit emirp pair

Print[DateString[]];
c=0;While[c++;
PrimeQ[IntegerReverse[r=RandomPrime[{10^4999,2*10^4999}]]]==False];
Print[{DateString[], c}]; r

Tue 24 Mar 2026 13:20:15

{Thu 2 Apr 2026 14:16:15, 1459}

13734728109222387308771911883098209504266491220378415449228996256958556204646209255426997204731352359449756449041282911838827753960110717667741546300796170994606405370205525990467395376009947818863867098443204707446280728853460347596959087028624624873124154773387129505731773658548559945072217868331005644146148486987796403656801876947383547342120251584407014371145256380254312563183866535417598667871824487793918102277168404192702988592723616031279706185729027937193115459363751801100834619648559534755862280622532330328020545564913373716599937718339772157065308727535050239049475309383701181923039664677398022448040478292058445782572749973954471541202254146634154863136377224819621843776574351493423099417717302803582947518052391674365890421676801423682263895436033477349103616708548394962338144244739840618759795636515556851999913235196980652229399132598337576053168937606823091007475684552339301961892031641961714248878071017023578324887088755960213127771073546703472455657291745675975849520494469065429206686852364253408177225968538981379921456249713012719550869982628800215250141536070000956939408031634199798833269213339776024607090221636520868945020007583404435400304984816689218801098149473216367358358482560919964155113665854879162787733470212782577499299460614936316249501982462197582182962661480246316492791906606967203513849810898912521723364783300800397527161480006666132471635152505857552637781618190671943929866125374286353526295866879589156528069268446360659588156073182367126878655885846017841827594449729142868018298455042670803762560261034102071781850653996720652827866216113764531977499870831481877699820219265369589791816326483849854098097404115191627985774704862207480350650524253157202313714981369031023817964668976804563887152280560591825099628968174198256928594455474900614206201208779564019513967006148424961575107554035816503265109246522149031864758498683614882701625685700872773227021642782062868941145310351815390646299885415571562126969030978677691992248131837773010974896587969945625215247802998599555149844869576921906654915655378310960741531349433956427372335169637595119451916257126526280015229284620103272436514641785833667906959477216083771551052106172820461661921196270515411038383894689853536962945436545227700069617650926512319248691302624136735627062344420181527288419813974095715282212691583319754787733622431421874596766566781210035118902671019438169295573224505091585397715351315220211971040233736523974341495533949868364720277377782599728157350029382463638680674321687547356330765388203811846145371779763392852911636547647481956184757017178391537543535061700390946825273445872542682841891167992835988152856822682714317459393194812472058333096943727715717938929497658790667620293930654794830364719577049887208648521075972113202459509425634726291406990514668964980723429065928682562597336923568312002853777432281023039930293635129199440948687280466516218157232869951411288874973458368152724148075445625803015700585387849533731143257417116714188837383227808909962194283481216500073402466043334005782482811768333556062299980861037631738960230903988141466474914973109939569029008994447469841264687420328226975199672037910132356689256318605922099489971249725724478498782743882782690449251101947062584707755445477591011686309629814598618824681005820262188651690555030066130820115706496744154662972097838464620864109248150554977389731984069894739940147765980248175151267385448245010741453588017824020636560200828952438588646996716310593319136256633679956860537422448902141226501877981016117706838811826647919831942614642062404688464031914722034158404047771516715512437734236041562161536854739816352115170865325632600798156951738783115882250368309347812703075264217063439654304694709966393200029975921707823139029998209103051390416799743854828992885437521880547367118888862322413374719343146756530741790302078652676659228463250342071145099375265620764389943047611045428183649445593679065081627297218931027072918317542023094964352985593971204351149921620655199890626051131805882424498700115214465774587948209887902292657524952455402231405821109075638114959572631886949305122157028523531876233977699646931396075719474191681597682924071799804008775563101404661918081796360660189113306106394092364326877126214067888878532744860157995659689449232748995366653945094234108364647434237692992245404080070494425022553082178108569582011506349785726297495243949030211388665827342268742694968604680029493370744659894200765912072030956961758839895603163676944756552653917173731760257052296666264677111508448519434784124629839512816675234329603341834304686287860364334731171629288773512175476941081385777926407651284584960519842623921169707152430953904143362518957259889371822834194124362865942682637039390381181943090487239006104649608076772200752347770219391585047496141065719922022050533141603543274273449631439746074641670898190472653657991251980586966500792504004728827518312237017772593842641588253316664038908417318413936902013666661226800919070758421595913214002598621253

IntegerReverse[r]

35212689520041231959512485707091900862216666631020963931481371480983046661335288514624839527771073221381572882740040529700566968508915219975635627409189807614647064793413694437247234530614133505022022991756014169474058519391207774325700227767080694640160093278409034918118309393073628624956826342149143822817398895275981526334140935903425170796112932624891506948548215670462977758318014967457121537788292617113743346306878268640343814330692343257661821593892642148743491584480511177646266669225075206713737171935625565744967636130659893885716965903027021956700249895644707339492008640686949624786224372856688311203094934259479262758794360511028596580187128035522052449407008040454229929673243474646380143249054935666359984723294498695659975106844723587888876041262177862346329049360160331198106606369718081916640410136557780040899717042928679518619147491757069313964699677933267813532582075122150394968813627595941183657090112850413220455425942575629220978890284978547756441251100789442428850813115062609899155602612994115340217939558925346949032024571381927072013981279272618056097639554494638182454011674034998346702656257399054117024305236482295667625687020309714703565764134391747331422326888881176374508812573458829982845834799761409315030190289992093132870712957992000239366990749640345693436071246257030721874390386305228851138783715965189700623652356807151125361893745863516126514063243773421551761517774040485143022741913046488640426024641624913891974662811883860771161018977810562214120984422473506865997633665263191339501361769964688583425982800206563602042871088535414701054284458376215157184208956774104993749896048913798377945505184290146802646483879027926645144769460751102803166003055509615688126202850018642881689541892690368611019577454455770748526074910115294409628728834728789487442752794217998499022950681365298665323101973027699157962282302478646214896474449980092096593990137941947466414188930903206983713673016808999226065533386711828428750043334066420437000561218438249126990980872238373888141761171475234113733594878358500751030852654457084142725186385437947888211415996823275181261566408278684904499192153639203993032018223477735820021386532963379526528682956092432708946986641509960419262743652490595420231127957012584680278894077591746303849745603939202676609785679492983971751772734969033385027421849139395471341728622865825188953829976119814828624527854437252864909300716053534573519387171075748165918474674563611925829336797717354164811830288356703365374578612347608683636428392005375182799528777377202746386894933559414347932563733204017911202251315351779358519050542237559296183491017620981153001218766566769547812413422633778745791338519621228251759047931891488272518102444326072653763142620319684291321562905671696000772254563454926963535898649838383011451507269112916616402827160125015517738061277495960976633858714641563427230102648292251008262562175261915491159573696153327372465933494313514706901387355651945660912967596844894155599589920874251252654996978569847901037773813184229919677687903096962126517551458899264609351815301354114986826028724612072237727800758652610728841638689485746813094122564290156230561853045570157516942484160076931591046597780210260241600947455449582965289147186982699052819506508225178836540867986646971832013096318941731320275135242505605308470226840747758972619151140479089045894838462361819798596356291202899677818413807899477913546731161266872825602769935605818717020143016206526730807624055489281086824192794449572814871064858855687862176328137065188595606364486296082565198597866859262535368247352166892934917609181618773625575850525153617423166660008416172579300800338746332712521989801894831530276960660919729461364208416626928128579126428910594261363941606499299477528721207433778726197845856631155146991906528485385376361237494189010881298661848940300453440438570002054986802563612209070642067793331296233889799143613080493965900007063514105251200882628996805591721031794265412997318983586952277180435246325868660292456096449402594857957654719275655427430764537017772131206955788078842387532071017087884241716914613029816910393325548657470019032860673986135067573389523199392225608969153231999915865551563659795781604893744244183326949384580761630194377433063459836228632410867612409856347619325081574928530820371771499032439415347567734812691842277363136845143664145220214517445937994727528754485029287404084422089377646693032918110738390357494093205053572780356075127793381773999561737331946554502082303323522608226855743595584691643800110815736395451139173972092758160797213061632729588920729140486177220181939778442817876689571453566838136521345208365254117341070448515202124374538374967810865630469778968484164144650013386871227054995584585637713750592178337745142137842642682078095969574306435882708264470740234489076836881874990067359376409952550207350460649907169700364514776671701106935772883811928214094465794495325313740279962455290264640265585965269982294451487302219466240590289038811917780378322290182743731

Click on either number to check its primality.

A random 2000-digit emirp pair

Print[DateString[]];
c=0; While[c++; PrimeQ[IntegerReverse[r=RandomPrime[{10^1999,2*10^1999}]]]==False];
Print[{DateString[], c}]; r

Mon 23 Mar 2026 16:19:04

{Mon 23 Mar 2026 18:37:09, 305}

14855218387530938731264800899806518554251409448753318067281617721104517975019660570816502191121802141387619791604557638640603077054520997318307203718761757739257990957393586487037638214729490346907077085366489735302991920794042479840185960548800113792237378778189700214336498150535494706550605947647886952709343445154850786791334376804237058351294799668452160206131345032141325576891497636422462012076224432607954324056613347607288129441043897934814166919553140730183934337952784895386915184278773673374499327984879217657567333750360009291505056111578053084511773793397248168145190194638081779158080985373127557284411266286462358754778798450217253924795704562031795767586150594858361787012654211320033792723983297048174107728830987370130777266997038517867493302588134280307951436792574170079530221417396081625730302595728237532318481405855540975409890906976902320267307459218191770761431037983144020890302946754575512111129239578508080696921714584513835630889334839362187530001616420174589110874531666851407830633657753457085270606608334710585505853591828745779378101187982074326317494916222176946818501389870085531903573860851057307085813978075441446820544507426572075052156092931837527279166150509917972776167153657340031646179631733906184205918255895475754364175238057482645899534235102077183676796749323690141704894319808779172119291942162868677765137547565809194418652476017816016763486268007290212946536413065587272480288193061788482406655351702586154143963745149534333768316994754590468906962685037527510130840705726077739498669858651281009519862797180044407205030051742292526137434721833180012034655794438599828098375237119761007728650703770787960212849241788574933755087711157262236337487014829313684940715849983628697605605634086992019999606613109048737110152003061306410080888361354585657807374315692388968946536330992803388106574848702486355828678460394253967147711575515270818557921500146950778382811866201918398021331397625888200120115790700195112386497426010970976957364112704151652043

IntegerReverse[r]

34025615140721146375967907901062479468321159100709751102100288852679313312089381910266811828387705964100512975581807251557511774176935249306487682855368420784847560188330829903363564986988329651347370875658545316388808001460316030025101173784090131660699991029968043650650679682638994851704948631392841078473363226275111778055733947588714294821206978707730705682770016791173257389082899583449755643021008133812743473162529224715003050270444008179726891590018215685896689493777062750704803101572573058626960986409545749961386733343594154736934145168520715355660428488716039188208427278556031463564921209270086268436761061871067425681449190856574573156777686826124919291127197780891349840714109632394769767638177020153243599854628475083257146345757459855281950248160933713697164613004375635176167727971990505166197272573813929065125057027562470544502864414457087931858070375015806837530913558007898310581864967122261949471362347028978110187397754782819535850558501743380660607258075435775633603870415866613547801198547102461610003578126393843398803653831548541712969608080587593292111121557545764920309802044138973013416707719181295470376202320967960909890457904555850418481323573282759520303752618069371412203597007147529763415970308243188520339476871583079966277703107378903882770147184079238932729733002311245621078716385849505168576759713026540759742935271205489787745785326468266211448275572137358908085197718083649109154186184279339737711548035087511165050519290006305733376575671297848972399447337637787248151968359848725973343938103704135591966141843979834014492188270674331665042345970623442267021026422463679419867552314123054313160206125486699749215385073240867343319768705845154434390725968874674950605560749453505189463341200798187787373229731100884506958104897424049702919920353798466358077070964309492741283673078468539375909975293775716781730270381379902545077030604683675540619791678314120812119120561807506691057971540112771618276081335784490415245581560899800846213783903578381255841

Click on either number to check its primality.

A random large emirp pair

One might think from my previous post that large base-ten emirps congregate near — or at least involve —  powers of ten. Well, record ones certainly do but that is surely an artifact of the convenience of searching for such integers in those locations, expressing them without having to show all of their digits, and even proving their primality.

I recently found that Mathematica has a RandomPrime function which can be configured to generate primes with a specific number of digits. By repeated application of it and checking each against the primality (most often lack-of-primality) of the integer created by reversing its decimal digits, I can now create random emirps.

While[PrimeQ[IntegerReverse[r = RandomPrime[{10^999, 10^1000}]]] == False]; r

3279288520829477235642879267287999159015788532533738855066046440495522398413879852102369701530100869580838076083149157548206285059151203914266414912431580164820025933969565023665242290427065104497454406152915882315883324964117545072539206755054402862798019415649139491569247916954175149446689650326543522910485350967102290630555006513883295579511863580034048864302120190250042483217978026251237207016901362308898161048199473494827584506196053490289923397647958362118557321048941198888848619470770742015547396263817662528411868482723797066437421483218035169802940903987225108903574471943089572864902145297776096342849868617007993544349744145780223402039236076990018520939944400626427281300176781542771736168164872520396475344293444882067084862153824121702601618059184428161120858343524815906494130051717507462817874659446095816309231120150861019479629358822063445459770400310760092233488204681637298530785169163900358943079863912831713129072815997830914582590098549219524593979172161769855800664064007

The reverse of this is:

7004604660085589671612719793954259129458900952854190387995182709213171382193689703498530093619615870358927361864028843322900670130040779545443602288539269749101680510211329036185906449564787182647057171500314946095184253438580211618244819508161062071214283512684807602884443924435746930252784618616371772451876710031827246260044499390258100996706329302043220875414479434453997007168689482436906777925412094682759803491744753098015227893090492089615308123841247346607973272848681148252667183626937455102470770749168488888911498401237558112638597467933299820943506916054857284943749918401618988032631096107027321526208797123842400520910212034688404300853681159755923883156005550360922017690535840192253456230569866449415714596197429651949319465149108972682044505576029352705457114694233885132885192516044547944015607240922425663205659693395200284610851342194146624193021519505826028457519413806708380859680010351079632012589783148932255940446406605588373352358875109519997827629782465327749280258829723

I did not think that I would be able to prove their primality, but factordb (click on either number to see its evaluation there) apparently has some "elves" who download the smallest probable primes in the database and run deterministic tests on them. I guess I got lucky.

Some recent large emirps

Let it be understood that all emirps come in pairs, say (p, q) where the number of (decimal) integer digits of p and of q are identical, but p < q. Since, in the following, we are dealing with record large integers, I will explicitly state the value of q, the larger of the pair, followed by a linked p in square brackets.

In 2007, Jens Kruse Andersen noted the 10007-digit 10^10006+941992101*10^4999+1 [p] as the then-largest-known emirp. Eighteen years later, Stephan Schöler managed to up this by four decimal digits with his 3867632931*10^10001+1 [p]. One month ago today, this was highlighted in an episode of Numberphile, precipitating (of course) a couple of new records:

Two days after the video, gamer Gelly Gelbertson found 10^10056+10^6692+10^5872+1 [p] (a 10057-digit term in OEIS A393530). Another two days and Vishwath Ganesan discovered 10^20000+518406362*10^9996+1 [p] (a 20001-digit emirp). As Vish's record was not initially noted beyond his PrimeGrid Discord chat, it created, unfortunately, a large number of claims of record that were (being fewer than 20001 digits and coming after February 20) not actually records. That included a 10069-digit (still not proven) random emirp made possible by AI.

Updates

March 19: Serge Batalov captured a near-repunit 10^22822-10^63-1 [p] emirp.

March 26: Justin Auger posted 10^39988+5417497422*10^19990+1 [p].

March 27: Serge Batalov posted 10^47253-22*10^21607-1 [p].

April 6: Ryan Propper & Serge Batalov claim 10^77763-4*10^25683-1 [p].

April 19: Ryan Propper & Serge Batalov claim 10^111956-7*10^53855-1 [p].

Email me if you spot any errors or have something to add.

Within You Without You (cover)

War (on Iran). What is it good for?