cp's OEIS Frontend

A030547 Number of terms (including the initial term) needed to reach a palindrome when the Reverse Then Add! map (x -> x + (x-with-digits-reversed)) is repeatedly applied to n, or -1 if a palindrome is never reached.

%I A030547 #19 Feb 16 2025 08:32:35
%S A030547 1,1,1,1,1,1,1,1,1,2,1,2,2,2,2,2,2,2,3,2,2,1,2,2,2,2,2,3,2,2,2,2,1,2,
%T A030547 2,2,3,2,3,2,2,2,2,1,2,3,2,3,3,2,2,2,2,2,1,2,3,3,4,2,2,2,2,3,2,1,3,4,
%U A030547 5,2,2,2,3,2,3,3,1,5,7,2,2,3,2,3,3,4,5,1,25,2,3,2,3,3,4,5,7,25
%N A030547 Number of terms (including the initial term) needed to reach a palindrome when the Reverse Then Add! map (x -> x + (x-with-digits-reversed)) is repeatedly applied to n, or -1 if a palindrome is never reached.
%C A030547 It is conjectured that a(196) is the smallest term equal to -1. See A023108.
%D A030547 Daniel Lignon, Dictionnaire de (presque) tous les nombres entiers, Ellipses, Paris, 2012, 702 pages. See Entry 196.
%H A030547 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/196-Algorithm.html">196 Algorithm.</a>
%t A030547 Table[Length@
%t A030547   NestWhileList[# + IntegerReverse[#] &, n, ! PalindromeQ[#]  &], {n, 98}] (* _Robert Price_, Oct 18 2019 *)
%Y A030547 Cf. A006960, A023108, A063018, etc.
%Y A030547 Equals A033665(n) + 1.
%K A030547 nonn,base
%O A030547 1,10
%A A030547 _Eric W. Weisstein_
%E A030547 Edited by _N. J. A. Sloane_, May 09 2015