A001520 a(n) = (6*n+1)*(6*n+3)*(6*n+5).

15, 693, 3315, 9177, 19575, 35805, 59163, 90945, 132447, 184965, 249795, 328233, 421575, 531117, 658155, 803985, 969903, 1157205, 1367187, 1601145, 1860375, 2146173, 2459835, 2802657, 3175935, 3580965, 4019043, 4491465, 4999527, 5544525, 6127755, 6750513

Offset

0,1

Links

T. D. Noe, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

Formula

From Jaume Oliver Lafont, Oct 20 2009: (Start)

G.f.: 3*(1+x)*(5+206*x+5*x^2)/(1-x)^4.

Sum_{k>=0} 1/a(k) = log(3)/16. (End)

a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n >= 4. - Jinyuan Wang, Mar 10 2020

Sum_{n>=0} (-1)^n/a(n) = Pi/48. - Amiram Eldar, Sep 22 2022

Maple

A001520:=n->(6*n+1)*(6*n+3)*(6*n+5); seq(A001520(n), n=0..50); # Wesley Ivan Hurt, Mar 10 2014

Mathematica

Table[(6n+1)(6n+3)(6n+5), {n, 0, 50}] (* Wesley Ivan Hurt, Mar 10 2014 *)

Prog

(PARI) a(n)=(6*n+1)*(6*n+3)*(6*n+5) \\ Charles R Greathouse IV, Oct 18 2022

Crossrefs

Sequence in context: A266519 A177230 A209499 * A062079 A062032 A204251

Adjacent sequences: A001517 A001518 A001519 * A001521 A001522 A001523

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved