A157024 a(0)=1, a(n) = (3n-1)*3n*(3n+1)/2 for n>0.

1, 12, 105, 360, 858, 1680, 2907, 4620, 6900, 9828, 13485, 17952, 23310, 29640, 37023, 45540, 55272, 66300, 78705, 92568, 107970, 124992, 143715, 164220, 186588, 210900, 237237, 265680, 296310, 329208, 364455, 402132, 442320, 485100, 530553, 578760, 629802

Offset: 0

Author

Jaume Oliver Lafont, Feb 21 2009

Keywords

• nonn

Crossrefs

Cf. A002391, A027480, A058962, A097321, A154920.

Programs

Mathematica

nxt[{n_,a_}]:={n+1,((3n)(3n-1)(3n+1))/2}; NestList[nxt,{0,1},40][[All,2]]/.(0->Nothing) (* Harvey P. Dale, Sep 24 2016 *)

Formula

Sum_{n>=0} 1/a(n) = log(3).

G.f.: (1+8x+63x^2+8x^3+x^4)/(1-x)^4.

a(n) = A027480(3n-1), n>0. - R. J. Mathar, Apr 07 2009

Sum_{n>=0} (-1)^n/a(n) = 4*log(2)/3. - Amiram Eldar, Feb 27 2022