A254857 Octagonal numbers (A000567) that are also centered heptagonal numbers (A069099).

1, 8, 736, 5461, 496133, 3680776, 334392976, 2480837633, 225380369761, 1672080883936, 151906034826008, 1126980034935301, 102384442092359701, 759582871465509008, 69006962064215612536, 511957728387718136161, 46510590046839230489633, 345058749350450558263576

Offset: 1

Author

Colin Barker, Feb 08 2015

Keywords

• nonn
• easy

Examples

			736 is in the sequence because it is the 16th octagonal number and the 15th centered heptagonal number.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..708
• Index entries for linear recurrences with constant coefficients, signature (1,674,-674,-1,1).

Crossrefs

Cf. A000567, A069099, A254855, A254856.

Programs

PARI

Vec(-x*(x^4+7*x^3+54*x^2+7*x+1)/((x-1)*(x^2-26*x+1)*(x^2+26*x+1)) + O(x^100))

Formula

a(n) = a(n-1)+674*a(n-2)-674*a(n-3)-a(n-4)+a(n-5).

G.f.: -x*(x^4+7*x^3+54*x^2+7*x+1) / ((x-1)*(x^2-26*x+1)*(x^2+26*x+1)).