A258129 Octagonal numbers (A000567) that are the sum of three consecutive octagonal numbers.

698901, 5102520783381, 37252493940331837461, 271973082264557457061125141, 1985621622943208359132836202790421, 14496630316026749501691464257547633057301, 105837027604506739193825102426073141683789429781, 772695182809023513889440668692977953487035688873891861

Offset: 1

Author

Colin Barker, May 21 2015

Keywords

• nonn
• easy

Examples

			698901 is in the sequence because Oct(483) = 698901 = 231296 + 232965 + 234640 = Oct(278) + Oct(279) + Oct(280).
		

Links

• Colin Barker, Table of n, a(n) for n = 1..145
• Index entries for linear recurrences with constant coefficients, signature (7300803,-7300803,1).

Crossrefs

Cf. A000567, A258128, A258130, A258131, A258132.

Programs

Mathematica

CoefficientList[Series[-21*x*(x^2 -844482*x +33281)/((x-1)*(x^2 -7300802*x +1)), {x, 0, 50}], x] (* G. C. Greubel, Oct 18 2017 *)
LinearRecurrence[{7300803,-7300803,1},{698901,5102520783381,37252493940331837461},20] (* Harvey P. Dale, Sep 16 2018 *)

PARI

Vec(-21*x*(x^2 -844482*x +33281)/((x-1)*(x^2 -7300802*x +1)) + O('x^20))

Formula

G.f.: -21*x*(x^2 -844482*x +33281)/((x-1)*(x^2 -7300802*x +1)).