Saturday, October 27

A long loop

Eric Angelini's digit-difference/add-subtract/iterate procedure, to which I drew attention two weeks ago, continues to delight. I knew there was a length-25 loop starting with 20971:

 0 20971
 1 50232
 2 102345
 3 223459
 4 212312
 5 101102
 6 211223
 7 110212
 8 98101
 9 80983
10 170138
11 841395
12 408752
13 889984 *maximum
14 879840
15 758392
16 522717
17 217055
18 49552
19 103584
20 235927
21 111172
22 110521
23 95211
24 52103
25 20971

Now I have discovered a significantly longer loop starting with 204099163.

Update (3 Nov 2012): There exists an intermediate length-85 loop starting with 17175432.

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