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 A115657 Both k and the reverse of k are pentagonal numbers (A000326). 0
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified August 2 21:27 EDT 2024. Contains 374875 sequences. (Running on oeis4.)