A258132 Octagonal numbers (A000567) that are the sum of fifteen consecutive octagonal numbers.

4715040, 8463840, 1122749669280, 2015496399840, 267373851637578960, 479974343542849680, 63672943775553479639280, 114302050117965712710960, 15163202176330482896520455040, 27220118818712616412771202880, 3610995292612020914167620625112640

Offset: 1

Author

Colin Barker, May 21 2015

Keywords

• nonn
• easy

Examples

			4715040 is in the sequence because Oct(1254) = 4715040 = 300833 + 302736 + 304645 + 306560 + 308481 + 310408 + 312341 + 314280 + 316225 + 318176 + 320133 + 322096 + 324065 + 326040 + 328021 = Oct(317) + ... + Oct(331).
		

Links

• Colin Barker, Table of n, a(n) for n = 1..370
• Index entries for linear recurrences with constant coefficients, signature (1,238142,-238142,-1,1).

Crossrefs

Cf. A000567, A258128, A258129, A258130, A258131.

Programs

Mathematica

CoefficientList[Series[-240*x*(7*x^4 +4*x^3 -449376*x^2 +15620*x +19646)/((x-1)*(x^2 -488*x +1)*(x^2 +488*x +1)), {x, 0, 50}], x] (* G. C. Greubel, Oct 18 2017 *)

PARI

Vec(-240*x*(7*x^4 +4*x^3 -449376*x^2 +15620*x +19646)/((x-1)*(x^2 -488*x +1)*(x^2 +488*x +1)) + O('x^20))

Formula

G.f.: -240*x*(7*x^4 +4*x^3 -449376*x^2 +15620*x +19646)/((x-1)*(x^2 -488*x +1)*(x^2 +488*x +1)).