A254676 Heptagonal numbers (A000566) which are also centered triangular numbers (A005448).

1, 235, 2839, 902101, 10906669, 3465871039, 41903418691, 13315875628969, 160992923703385, 51159590700627091, 618534770964985711, 196555134155933653885, 2376410429054551397509, 755164774267506397598311, 9130168249892815504243099, 2901342866180625423639056209

Offset: 1

Author

Colin Barker, Feb 05 2015

Keywords

• nonn
• easy

Examples

			235 is in the sequence because it is the 10th heptagonal number and the 13th centered triangular number.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..558
• Index entries for linear recurrences with constant coefficients, signature (1,3842,-3842,-1,1).

Crossrefs

Cf. A000566, A005448, A254674, A254675.

Programs

Mathematica

LinearRecurrence[{1,3842,-3842,-1,1},{1,235,2839,902101,10906669},20] (* Harvey P. Dale, Oct 12 2024 *)

PARI

Vec(-x*(x^4+234*x^3-1238*x^2+234*x+1)/((x-1)*(x^2-62*x+1)*(x^2+62*x+1)) + O(x^100))

Formula

a(n) = a(n-1)+3842*a(n-2)-3842*a(n-3)-a(n-4)+a(n-5).

G.f.: -x*(x^4+234*x^3-1238*x^2+234*x+1) / ((x-1)*(x^2-62*x+1)*(x^2+62*x+1)).