A068667 a(1) = 7; a(n) = smallest palindromic multiple of a(n-1).

7, 77, 616, 6776, 88088, 616616, 232464232, 21154245112, 232696696232, 21175399357112, 21154245133154245112, 232696696464696696232, 21175399378287399357112, 63386501441764911946714410568336

Offset: 1

Author

Amarnath Murthy, Mar 01 2002

Keywords

• base
• nonn

Crossrefs

Cf. A068664 (from a(6) on) and this sequence (from a(3) on) coincide.

Cf. A068664, A068665, A068666, A068668, A070069, A068971, A068972, A068973, A068974.

Programs

Mathematica

a[1] = 7; a[n_] := a[n] = Block[{k = 2}, While[k*a[n - 1] != ToExpression[ StringReverse[ ToString[k*a[n - 1]]]], k++ ]; k*a[n - 1]]; Table[a[n], {n, 1, 14}]
NestList[Module[{k=2},While[!PalindromeQ[k #],k++];k #]&,7,10] (* The program generates the first 11 terms of the sequence. *) (* Harvey P. Dale, Feb 07 2025 *)

Extensions

Last two terms from David W. Wilson, Sascha Kurz and edited by Patrick De Geest, Mar 30 2002