A115657 Both k and the reverse of k are pentagonal numbers (A000326).

0, 1, 5, 22, 210, 287, 782, 1001, 2882, 7740, 15251, 77180, 565187, 720027, 781565, 7081807, 7451547, 26811862, 54177145, 206489067, 246214610, 760984602, 1050660501, 1085885801, 1528888251, 2642326276, 2911771192, 6726232462, 24375132126, 62123157342

Offset: 1

Author

Giovanni Resta, Jan 28 2006

Keywords

• base
• nonn

Examples

			565187=P(614) and 781565=P(722), where P(k) = k*(3*k-1)/2 is the k-th pentagonal number.
		

Crossrefs

Cf. A000326, A061455, A061457.

Programs

PARI

lista(nn) = for (n=0, nn, my(P = n*(3*n-1)/2); if (ispolygonal(fromdigits(Vecrev(digits(P))), 5), print1(P, ", "));); \\ Michel Marcus, May 22 2022

Extensions

0 and additional terms from Jon E. Schoenfield, May 22 2022