A259164 Positive heptagonal numbers (A000566) that are squares (A000290) divided by 2.

18, 1877922, 194706720450, 20187582187830642, 2093088896203949915058, 217015642916030352905224578, 22500615886726770153715544792802, 2332908856150589340161504762302084050, 241880656000904788079898366611289133690962

Offset

1,1

Comments

Intersection of A000566 and A001105 (even squares divided by 2). - Michel Marcus, Jun 20 2015

Links

Colin Barker, Table of n, a(n) for n = 1..200

Index entries for linear recurrences with constant coefficients, signature (103683,-103683,1).

Formula

G.f.: -18*x*(x^2+646*x+1) / ((x-1)*(x^2-103682*x+1)).

Example

18 is in the sequence because 18 is the 3rd heptagonal number, and 2*18 is the 6th square.

Mathematica

LinearRecurrence[{103683, -103683, 1}, {18, 1877922, 194706720450}, 20] (* Vincenzo Librandi, Jun 20 2015 *)

Prog

(PARI) Vec(-18*x*(x^2+646*x+1)/((x-1)*(x^2-103682*x+1)) + O(x^20))

Crossrefs

Cf. A000290, A000566, A001105, A259156-A259163, A259165-A259167.

Sequence in context: A078352 A215577 A071098 * A013808 A115479 A144838

Adjacent sequences: A259161 A259162 A259163 * A259165 A259166 A259167

Keyword

nonn,easy

Author

Colin Barker, Jun 19 2015

Status

approved