A259158 Positive triangular numbers (A000217) that are heptagonal numbers (A000566) divided by 2.

171, 355817826, 739874066553765, 1538466018777014327028, 3199027777735470191011289295, 6651936797966044301302839516949686, 13831784604089070782667939513452521937961, 28761287297921206463992005998270360082445758120

Offset: 1

Author

Colin Barker, Jun 19 2015

Keywords

• nonn
• easy

Examples

			171 is in the sequence because 171 is the 18th triangular number, and 2*171 is the 12th heptagonal number.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..158
• Index entries for linear recurrences with constant coefficients, signature (2079363,-2079363,1).

Crossrefs

Cf. A000217, A000566, A259156, A259157, A259159-A259167.

Programs

Mathematica

LinearRecurrence[{2079363, -2079363, 1}, {171, 355817826, 739874066553765}, 20] (* Vincenzo Librandi, Jun 20 2015 *)

PARI

Vec(-171*x*(1443*x+1) / ((x-1)*(x^2-2079362*x+1)) + O(x^20))

Formula

G.f.: -171*x*(1443*x+1) / ((x-1)*(x^2-2079362*x+1)).