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 A072718 #6 Sep 27 2017 11:48:15 %S A072718 118722683079,138346366158,178574614218,277673713317,316920881277, %T A072718 336544564356,435643663455,455267148336,614218178574,633841861653, %U A072718 713317277673,851663544732 %N A072718 Numbers n such that 12 applications of 'Reverse and Subtract' lead to n, whereas fewer than 12 applications do not lead to n. %C A072718 There are 12 twelve-digit terms in the sequence. Further terms are obtained (a) by inserting at the center of these terms either any number of 0's (for 178574614218, 277673713317, 614218178574, 713317277673) or any number of 9's (for the other eight terms) 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. %F A072718 n = f^12(n), n <> f^k(n) for k < 12, where f: x -> |x - reverse(x)|. %e A072718 118722683079 -> 851663544732 -> 614218178574 -> 138346366158 -> 713317277673 -> 336544564356 -> 316920881277 -> 455267148336-> 178574614218-> 633841861653-> 277673713317-> 435643663455-> 118722683079. %Y A072718 Cf. A072137, A072141, A072142, A072143, A072719. %K A072718 base,nonn %O A072718 1,1 %A A072718 _Klaus Brockhaus_, Jul 15 2002