

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.


16



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
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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



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



KEYWORD

base,nonn


AUTHOR



STATUS

approved



