A092341 a(0)=1, a(n) = sigma_3(3n).

1, 28, 252, 757, 2044, 3528, 6813, 9632, 16380, 20440, 31752, 37296, 55261, 61544, 86688, 95382, 131068, 137592, 183960, 192080, 257544, 260408, 335664, 340704, 442845, 441028, 553896, 551881, 703136, 682920, 858438, 834176, 1048572, 1008324, 1238328, 1213632

Offset: 0

Author

N. J. A. Sloane, Mar 20 2004

Keywords

• nonn
• easy

Crossrefs

Trisection of A001158.

Cf. A013662, A045823, A091986, A092342, A092343.

Programs

Mathematica

Join[{1},DivisorSigma[3,3*Range[40]]] (* Harvey P. Dale, Feb 02 2012 *)

PARI

a(n) = if(n < 1, 1, sigma(3*n, 3)); \\ Amiram Eldar, Dec 12 2023

Formula

Sum_{k=1..n} a(k) ~ (83*zeta(4)/12) * n^4. - Amiram Eldar, Dec 12 2023