A254285 Hexagonal numbers (A000384) which are also centered triangular numbers (A005448).

1, 1891, 26335, 71156485, 991081981, 2677903145191, 37298379237211, 100780206894952201, 1403687203222107385, 3792762303606727977835, 52826364168762410080471, 142736816433155393822880781, 1988067387723517337746328821, 5371757345852607787523567324911

Offset

1,2

Links

Colin Barker, Table of n, a(n) for n = 1..437

Index entries for linear recurrences with constant coefficients, signature (1,37634,-37634,-1,1).

Formula

a(n) = a(n-1)+37634*a(n-2)-37634*a(n-3)-a(n-4)+a(n-5).

G.f.: -x*(x^4+1890*x^3-13190*x^2+1890*x+1) / ((x-1)*(x^2-194*x+1)*(x^2+194*x+1)).

Example

1891 is in the sequence because it is the 31st hexagonal number and the 36th centered triangular number.

Prog

(PARI) Vec(-x*(x^4+1890*x^3-13190*x^2+1890*x+1)/((x-1)*(x^2-194*x+1)*(x^2+194*x+1)) + O(x^100))

Crossrefs

Cf. A000384, A005448, A254283, A254284.

Sequence in context: A151773 A020321 A177086 * A035869 A045198 A020417

Adjacent sequences: A254282 A254283 A254284 * A254286 A254287 A254288

Keyword

nonn,easy

Author

Colin Barker, Jan 28 2015

Status

approved