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
Examples
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.
Programs
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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;
Comments