cp's OEIS Frontend

A070742 a(n) = index of the (presumably) last palindrome in the 'Reverse and Add' trajectory of n, or -1 if this number is not finite, or 0 if no palindrome exists.

%I A070742 #8 Jun 11 2024 22:23:52
%S A070742 18,17,32,16,36,31,30,15,23,35,34,30,33,29,29,14,32,22,28,34,30,33,29,
%T A070742 29,14,32,22,28,27,30,33,29,29,14,32,22,28,27,28,33,29,29,14,32,22,28,
%U A070742 27,28,26,29,29,14,32,22,28,27,28,26,13,29,14,32,22,28,27,28,26,13,27
%N A070742 a(n) = index of the (presumably) last palindrome in the 'Reverse and Add' trajectory of n, or -1 if this number is not finite, or 0 if no palindrome exists.
%C A070742 The computation of a trajectory was stopped, when within 1000 steps no further palindrome appeared. - A033665(n) + 1 is the index of the first palindrome in the 'Reverse and Add' trajectory of n.
%C A070742 Terms correct for at least 10000 steps after last palindrome. - _Sean A. Irvine_, Jun 11 2024
%H A070742 <a href="/index/Res#RAA">Index entries for sequences related to Reverse and Add!</a>
%e A070742 6, 33, 66, 363, 4884, 8836886388, 47337877873374 are the seven palindromes in the trajectory of 6 and the next 1000 steps do not lead to another palindrome; 47337877873374 is the 31st term in the trajectory, so a(6) = 31.
%o A070742 (ARIBAS) var st,nst: string; end; for k := 1 to 74 do n := k; j := 1; x := 0; c := 0; while c < 1000 do st := itoa(n); nst := ""; for i := 0 to length(st) - 1 do nst := concat(st[i],nst); end; rev := atoi(nst); if n = rev then c := 0; x := j; end; inc(c); n := n + rev; inc(j); end; write(x,"," ); end;
%Y A070742 Cf. A033665, A065001, A070743, A070744.
%K A070742 base,nonn
%O A070742 1,1
%A A070742 _Klaus Brockhaus_, May 03 2002