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

1,3

Links

Table of n, a(n) for n=1..30.

Example

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

Prog

(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

Crossrefs

Cf. A000326, A061455, A061457.

Sequence in context: A356773 A208804 A066866 * A066865 A183902 A005632

Adjacent sequences: A115654 A115655 A115656 * A115658 A115659 A115660

Keyword

base,nonn

Author

Giovanni Resta, Jan 28 2006

Extensions

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

Status

approved