This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072143 #14 Sep 24 2020 03:21:36 %S A072143 108811891188,115521884478,117611882388,125520874479,177781822218, %T A072143 215511784488,242351757648,248841751158,278882721117,428823571176, %U A072143 432244567755,442243557756,455663544336,602315397684,604405395594 %N A072143 Numbers n such that 22 applications of 'Reverse and Subtract' lead to n, whereas fewer than 22 applications do not lead to n. %C A072143 There are 22 twelve-digit terms in the sequence. Further terms are obtained (a) by inserting at the center of these terms any number of 9's and (b) by concatenating a term any number of times with itself and inserting an equal number of 0's at all junctures. Method (b) may be applied recursively to all terms. - Revised thanks to a comment from _Hans Havermann_, Jan 27 2004 %C A072143 All terms are divisible by 10999989. - _Hugo Pfoertner_, Sep 23 2020 %H A072143 Ray Chandler, <a href="/A072143/b072143.txt">Table of n, a(n) for n = 1..22</a> %F A072143 n = f^22(n), n <> f^k(n) for k < 22, where f: x -> |x - reverse(x)|. %e A072143 108811891188 -> 772386227613 -> 455663544336 -> 177781822218 -> 634446365553 -> 278882721117 -> 432244567755 -> 125520874479 -> 848957151042 -> 608805391194 -> 117611882388 -> 765676234323 -> 442243557756 -> 215511784488 -> 668975331024 -> 248841751158 -> 602315397684 -> 115521884478 -> 758966241033 -> 428823571176 -> 242351757648 -> 604405395594 -> 108811891188. %Y A072143 Cf. A072137, A072140, A072141, A072142, A072718, A072719. %K A072143 base,nonn %O A072143 1,1 %A A072143 _Klaus Brockhaus_, Jun 24 2002