A259078 Heptagonal numbers (A000566) that are other heptagonal numbers divided by 2.

6426, 9875715583923, 15176968126834688342280, 23323916081375479417207129139097, 35844119643974208514403771705730853759974, 55085128439364942192092971212729781713850848998511, 84654649223375294035879228202426981713600292140166013136308

Offset

1,1

Links

Colin Barker, Table of n, a(n) for n = 1..109

Index entries for linear recurrences with constant coefficients, signature (1536796803,-1536796803,1).

Formula

G.f.: -189*x*(x^2+1372105*x+34) / ((x-1)*(x^2-1536796802*x+1)).

Example

6426 is in the sequence because 6426 is the 51st heptagonal number, and 2*6426 is the 72nd heptagonal number.

Mathematica

LinearRecurrence[{1536796803, -1536796803, 1}, {6426, 9875715583923, 15176968126834688342280}, 20] (* Harvey P. Dale, May 17 2018 *)

Prog

(PARI) Vec(-189*x*(x^2+1372105*x+34)/((x-1)*(x^2-1536796802*x+1)) + O(x^20))

Crossrefs

Cf. A000566, A075528, A107736, A259079.

Sequence in context: A031578 A252612 A259060 * A104374 A222554 A104318

Adjacent sequences: A259075 A259076 A259077 * A259079 A259080 A259081

Keyword

nonn,easy

Author

Colin Barker, Jun 18 2015

Status

approved