Friday, February 6

(101*10^120072-87)/7 is prime

A good part of my dabbling in recreational arithmetic is searching for large primes. My previous best was 2*(10^39960+10^63+10^36+10^12)+2223 which has 39961 digits and dates to October 2011. Today I bettered that with (101*10^120072-87)/7 which is made up of 120074 digits — large enough to be on page three of Henri & Renaud Lifchitz's top probable prime records. The find arises out of an observation I made for A254005.

Friday, January 9

Coyotes

It's no secret that there are coyotes in Toronto. Over the years, neighbourhood acquaintances have told me they had seen one — generally down by the river, but just a few days ago in the local cemetery wherein a lot of folk walk/run their dogs. I don't always take my camera with me anymore — the way I used to when going for a walk — because having Bodie with me constrains my picture-framing ability. But this morning I did have my camera and certainly glad of it.

Initially, I spotted one coyote walking up the east side of Raymore Island:


A minute or so later, I noticed another one on the west side:


They both looked to be in good health, in spite of the bitter cold of the last few days. I like this more-distant capture of that second coyote rounding the upstream tip of the island:

Thursday, January 8

Replay


Twenty-five years ago I was still buying books, magazines, journals, and newsletters, as though I didn't know that the internet was just around the corner. Of course I didn't know. One of those newsletters was Cubism For Fun and there must have been a contest therein for me to have submitted to them an offbeat musical puzzle, complete with a mixtape. I never heard any more about it — until two days ago, when a Christian Halberstadt emailed me and asked if I was the author of it. I wasn't sure; it had been so long!

Unbeknownst to me, my "mystery" puzzle was published in 1997. Christian supplied me with a copy. He and his friend, Rolf Braun, had subsequently made an effort to solve it, or at least deconstruct some of the verbiage. Here is a reprint (with a few minor editorial accruements) of my 1990 submission to CFF:


Chet Ritter was a Mohawk from Kanesatake. He was young, handsome – but had a somewhat brutish attitude. He was well-educated; certainly well-read. He had trouble holding onto money, friends, or a place to live. However, unlike most people with that misfortune, he never succumbed to the despair and depravities of society’s outcasts. Instead, you could find him at the library – reading some mathematical journal and, headphones on, listening to some recent compact disc. (Remember when all you could find at a library was books?)

It was thus that I first met him some two years ago, listening to Bruce Cockburn’s Inner City Front and studying Raymond Smullyan’s Chess Mysteries of Sherlock Holmes. I placed in front of him a note on which I had written: CAN YOU CHAT? After turning around to look at me, but before removing his headphones, he crossed out my CAN, wrote underneath it the word KEN, placed quotation marks around the word CHAT, and printed his answer on the handed-back note: OUI. C’EST MOI! I must have looked a little puzzled, for he explained, “All my friends call me Cat.” I smiled as the joke sank in.

I think it was his witticism, this perversity, that attracted me to him… A child-like honesty in the face of come-what-may.

We had many delightful discussions on our haphazard encounters, detailing everything from the failings of democracy to the meaning of life. Much of what we dealt with were problems and puzzles in the realm of recreational mathematics. He was most interested in perusing a few of the less-well-known periodicals and newsletters to which I subscribed. I think he even wrote a couple of letters-to-the-editor to some of these.

Several months ago, he disappeared. He had lost his most recent part-time job, availing himself to the charities of one of his women-friends and spending the nights (near as I could tell) under a bridge by the river. Some weeks prior, he had handed me a slip of paper titled “DUODENE” on which were listed the following twelve items:

Who Cares?
School Days
Black Diamond Bay
10:15 Saturday Night
Me And The Boys
The Walk
Norwegian Wood
Get Off Of My Cloud
Planet Claire
Hurricane
The Magnificent Seven
Joey

I recognized at least a few of these as songs. In addition, Cat gave me a good-quality, blank 60-minute tape, saying simply, “You’ll need this.” I reacted to his generosity by asking, “Did you pay for this?” Cat shot back: “You gonna pay anybody for recording this music?” Embarrassed, I said no more.

It took a little doing, but I finally got that tape together. I had to have help however from a few of my more musically-inclined acquaintances; at least half of the songs (and three of the artists) were unknown to me. The first eight selections fit neatly on ‘side one’ of the tape. By this time I had a pretty good idea what the organizing principle was. ‘Side two’ confirmed my hunch although (I have to admit) I listened to Bob Dylan’s Hurricane three times before I heard it. When next I saw Cat, I gloated, “Some of the song-placings are context-sensitive. In fact Joey is downright ambiguous… You could have put it somewhere else.” Cat, grinning from ear to ear, jabbed a finger gently into my ribs and said, “But then, the songs wouldn’t have fit on the tape.”

That was a week before Cat’s disappearance and the second-last time I saw him. He never said good-bye but did mention a certain “home-sickness”. Life in the big city had (I think) gotten to him. “You know,” he once said, “this world is run by jerks for jerks.”

Thursday, January 1

Visitors from infinity

Sometimes a sequence in the OEIS doesn't do justice to the bigger picture. The blue trajectory, forward from the zero point to where it ends on the right is A251412. This integer sequence also has a backward history. Combined with an infinite number of like-minded sequences (four of which are shown; the identifying numbers at the forward end are the trajectories' minima at point zero) coming in from infinity at the left and going back out to it at the right, these trajectories meander for position in number space. Any outgoing trajectory running into an integer-point of an incoming one would of course merge with it. (Well, it was a single trajectory all along. We just didn't know it.) What if an outgoing trajectory were to run into its own tail? In that case, the trajectory is seen to be — not infinite — but finite. There are currently 34 known finite orbits in this mapping (which includes 7 fixed points, orbits of length 1). The currently longest orbit is one of length 91.

Wednesday, December 24

Pleasantly nonplussed

Eric Angelini suggested on Monday the sequence of numbers with the property that if one inserts a single plus anywhere inside them (and executes the additions) only primes result. In deference to the second part of the number-split not starting with it, he only allowed zero as a final digit:

11, 12, 14, 16, 20, 21, 23, 25, 29, 30, 32, 34, 38, 41, 43, 47, 49, 50, 52, 56, 58, 61, 65, 67, 70, 74, 76, 83, 85, 89, 92, 94, 98, 110, 112, 116, 118, 130, 136, 152, 158, 170, ...

Surely this sequence is finite. But what is the largest term? My program hinted that it might be the 11-digit 46884486265 (term #440), since it found no 12-digit representative. But (thankfully) I had the computation plod on:

5391391551358

5 + 391391551358 = 391391551363
53 + 91391551358 = 91391551411
539 + 1391551358 = 1391551897
5391 + 391551358 = 391556749
53913 + 91551358 = 91605271
539139 + 1551358 = 2090497
5391391 + 551358 = 5942749
53913915 + 51358 = 53965273
539139155 + 1358 = 539140513
5391391551 + 358 = 5391391909
53913915513 + 58 = 53913915571
539139155135 + 8 = 539139155143

All prime! By plugging 5391391551358 into Google, I discovered that this number was already known to Giovanni Resta, who treated the sequence from the perspective of allowing internal zeros. The numbers 20, 101, and 1001 appear to be (currently) missing from his magnanimous numbers list. But, he has one larger example:

97393713331910

9 + 7393713331910 = 7393713331919
97 + 393713331910 = 393713332007
973 + 93713331910 = 93713332883
9739 + 3713331910 = 3713341649
97393 + 713331910 = 713429303
973937 + 13331910 = 14305847
9739371 + 3331910 = 13071281
97393713 + 331910 = 97725623
973937133 + 31910 = 973969043
9739371333 + 1910 = 9739373243
97393713331 + 910 = 97393714241
973937133319 + 10 = 973937133329
9739371333191 + 0 = 9739371333191

Nice.

Wednesday, November 5

Das Ei des Columbus


Gabriel Fernandes' puzzle blog entry yesterday on the Logic Egg had me thinking about the Richter original called Ei des Columbus, which came out in 1893 to coincide with the 400th anniversary of Christopher Columbus' rediscovery of the Americas. Unbeknownst to me, Columbus' egg was then already a well-worn idiom in Germany, based on an apocryphal account of Columbus shaming his opponents by coming up with something outside the box. In short, Columbus' discovery is belittled by those present at a get-together who suggest that "any of us" could have found the New World. Columbus asks his detractors to stand an egg on its end, something that they are unable to accomplish. So he shows them how by gently hitting the egg onto the table so that its cracked shell now gives it support. Yes, he implores, any of us can do it.

Here is my transcription (I've shortened any long s occurrences but have left the sharp s as is) of the tale from Friedrich Förster's 1842 Christoph Columbus:

     Wir dürfen den Entdecker der neuen Welt nicht zur zweiten Fahrt dahin abreisen lassen, ohne jenes Gastmahles zu gedenken, bei welchem ein sinnreicher Einfall von ihm Veranlassung zu einem Sprüchworte wurde, welches eine eben so weite Verbreitung erhalten hat, wie sein welthistorischer Name; wer hörte nicht von dem Ei des Columbus? Bei einem Feste, welches der Cardinal Mendoza dem Admiral zu Ehren veranstaltete, hielt er ihm eine große Lobrede wegen der von ihm gemachten Endeckung, welche er den größten Sieg nannte, den jemals der Geist eines einzigen Mannes erfochten habe. Die anwesenden Herren vom Hofe nahmen es übel auf, daß einem Ausländer, noch dazu einem Manne, der nicht ein Mal von nobler Herkunst sei, so große Auszeichnung erwiesen würde. "Mich dünkt", bub einer der königlichen Kammerherren an, "der Weg nach der sogenannten neuen Welt war nicht so schwer zu finden, der Ocean stand überall offen und kein Spanischer Seefahrer würde den Weg verfehlt haben." Mit vornehmem Gelächter, hinter welches sich so gern die Dummheit verbirgt, gab die Gesellschaft dieser Aeußerung ihren Beifall zu erkennen und mehrere Stimmem riefen: "o, das hätte ein Jeder von uns gekonnt!"
     "Ich bin weit entfernt", entgegnete Columbus, "mir etwas als Ruhm anzumaßen, was ich nur einer gnädigen Fügung des Himmels zuschreiben darf; indessen kommt es doch bei vielen Dingen in der Welt, welche uns leicht auszuführen scheinen, oft nur darauf an, daß sie ein Anderer uns vormacht. Dürft’ ich", sagte Columbus zu jenem Kammerherrn gewendet, "Ew. Excellenz wohl ersuchen, dies Ei — er hatte sich von einem Diener ein Hühnerei bringen lassen — so auf die Spitze zu stellen, daß es nicht umfällt?" Die Excellenz versuchte von der einen, wie von der anderen Seite vergeblich, daß Ei zum Stehen zu bringen. Der Nachbar hat es sich aus, es gelang ihm eben so wenig; nun drängten sich die Anderen dazu, ein jeder wollte den Preis gewinnen, allein weder mit Eifer noch mit Ruhe war es möglich, das Kunststück auszuführen. "Es ist unmöglich!" riefen die Hidalgos, "Ihr verlangt Unausführbares!" — "Und doch", sagte Columbus, "werden diese Herren sogleich sagen: das kann ein Jeder von uns auch!" Jetzt nahm er das Ei, und setzte es mit einem leichten Schlag auf den Tisch, so daß es auf der eingedrückten Schale fest stand. — "Ja! das kann ein Jeder von uns!" riefen die Hidalgos; seitdem hört man oft sagen, wenn eine glückliche Erfindung gemacht wurde, zu welcher ein jeder sich klug genugt dünkt: "das Ei des Columbus!"

Sunday, October 12

Climb to a prime


I took on my table of A195264 three years ago. I am still chipping away at the currently-317 primary unknowns (out of 10000), extending ECM-factorization attempts from 2000 to 5000 curves. I'm not yet even half-way through the list. Occasionally factordb will have found for me (over time) the large factors for up to 116-digit composites! And in a handful of cases I have evolved an unknown into a prime — which finishes those unknowns from consideration, but there are plenty more.

I've been a little resentful that I hadn't picked the arguably aesthetically-better (one less arithmetic symbol with which to deal), historically better-known home prime sequence (A037274) on which to while away my time. No matter now: John Conway has offered $1000 for a resolution (problem 5) to term #20 of A195264, not term #49 of A037274 — which he could easily have picked instead. I don't believe that (mathematically) it makes any difference: one is as contrived as the other. Conway's point (I think) is that there exist easily-stated but impossible-to-prove conjectures about such sequences. To collect the $1000 for problem 5, you will almost certainly have to luck into a prime in the evolution, because proving that it doesn't evolve into a prime may well be impossible.

While the prize may spur some to further evolve A195265, it may also impede them from sharing any results of that effort. I hope that's not the case.

Friday, October 3

Time has come


My D5300 has a GPS chip in it. I don't own a mobile phone so this is actually my first acquaintance with the capability. Of course I enabled it, even though I suspect that it will be a drain on the camera's battery. As it turns out, only about one in seven of my photos had the location data embedded in it and a cursory look indicated location placement wasn't necessarily all that close. A handful of waypoints had me on the opposite side of the Humber river from where I actually was!

There is an upside. The camera has a set clock from satellite option and I had turned on this feature. The above photo was captured on September 28, exactly 19 days after my first photo taken just after I manually set the camera's clock. The photo's embedded time-stamp was still in sync with real time, indicated here by a website clock. I may never have to correct the camera clock again.

Wednesday, October 1

Shelfie


My new D5300 does some in-camera filter effects. My sense of photography is journalism — not art — so this seems to me extravagant and unnecessary. (If you want to photoshop, use a computer.) Regardless, I tried it out. This "shelfie" is a color sketch effect and its pastel hues are actually quite pleasant. I shared another shelfie on Google+ last year and there is some overlap with this image. The only other effect I have tried so far is HDR painting which was rather disappointing. I had hoped for better HDR and less painting.