A258128 Octagonal numbers (A000567) that are the sum of two consecutive octagonal numbers.

5461, 813281, 7272157205, 1083057360705, 9684433559760981, 1442322650052752161, 12896895753596262561301, 1920761265591267733640321, 17174976631595008767000306005, 2557904668044167195987033355105, 22872156829955018609383449248248341

Offset: 1

Author

Colin Barker, May 21 2015

Keywords

• nonn
• easy

Examples

			5461 is in the sequence because Oct(43) = 5461 = 2640 + 2821 = Oct(30) + Oct(31).
		

Links

• Colin Barker, Table of n, a(n) for n = 1..326
• Index entries for linear recurrences with constant coefficients, signature (1,1331714,-1331714,-1,1).

Crossrefs

Cf. A000567, A258129, A258130, A258131, A258132.

Programs

Mathematica

CoefficientList[Series[-x*(x^4 +20*x^3 -1146230*x^2 +807820*x +5461)/((x-1)*(x^2 -1154*x +1)*(x^2 +1154*x +1)), {x, 0, 50}], x] (* G. C. Greubel, Oct 18 2017 *)
LinearRecurrence[{1,1331714,-1331714,-1,1},{5461,813281,7272157205,1083057360705,9684433559760981},20] (* Harvey P. Dale, Feb 19 2018 *)

PARI

Vec(-x*(x^4 +20*x^3 -1146230*x^2 +807820*x +5461)/((x-1)*(x^2 -1154*x +1)*(x^2 +1154*x +1)) + O('x^20))

Formula

G.f.: -x*(x^4+20*x^3-1146230*x^2+807820*x+5461) / ((x-1)*(x^2-1154*x+1)*(x^2+1154*x+1)).