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

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

Offset: 1

Author

Colin Barker, Jun 19 2015

Keywords

• nonn
• easy

Comments

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

Examples

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

Links

• Colin Barker, Table of n, a(n) for n = 1..200
• Index entries for linear recurrences with constant coefficients, signature (103683,-103683,1).

Crossrefs

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

Programs

Mathematica

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

PARI

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

Formula

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