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.

18, 17, 32, 16, 36, 31, 30, 15, 23, 35, 34, 30, 33, 29, 29, 14, 32, 22, 28, 34, 30, 33, 29, 29, 14, 32, 22, 28, 27, 30, 33, 29, 29, 14, 32, 22, 28, 27, 28, 33, 29, 29, 14, 32, 22, 28, 27, 28, 26, 29, 29, 14, 32, 22, 28, 27, 28, 26, 13, 29, 14, 32, 22, 28, 27, 28, 26, 13, 27

Offset

1,1

Comments

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.

Terms correct for at least 10000 steps after last palindrome. - Sean A. Irvine, Jun 11 2024

Links

Table of n, a(n) for n=1..69.

Index entries for sequences related to Reverse and Add!

Example

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.

Prog

(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;

Crossrefs

Cf. A033665, A065001, A070743, A070744.

Sequence in context: A022974 A023460 A029926 * A304260 A176064 A278716

Adjacent sequences: A070739 A070740 A070741 * A070743 A070744 A070745

Keyword

base,nonn

Author

Klaus Brockhaus, May 03 2002

Status

approved