A144613 a(n) = sigma(3*n) = A000203(3*n).

4, 12, 13, 28, 24, 39, 32, 60, 40, 72, 48, 91, 56, 96, 78, 124, 72, 120, 80, 168, 104, 144, 96, 195, 124, 168, 121, 224, 120, 234, 128, 252, 156, 216, 192, 280, 152, 240, 182, 360, 168, 312, 176, 336, 240, 288, 192, 403, 228, 372, 234, 392, 216, 363, 288, 480, 260, 360

Offset: 1

Author

N. J. A. Sloane, Jan 15 2009

Keywords

• nonn
• easy
• changed

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..10000

Crossrefs

Sigma(k*n): A000203 (k=1), A062731 (k=2), this sequence (k=3), A193553 (k=4), A283118 (k=5), A224613 (k=6), A283078 (k=7), A283122 (k=8), A283123 (k=9).

Cf. A008585, A078708.

Programs

Mathematica

a[n_] := DivisorSigma[1, 3*n]; Array[a, 60] (* Amiram Eldar, Dec 16 2022 *)

PARI

vector(66, n, sigma(3*n, 1)) \\ Joerg Arndt, Jul 30 2011

Formula

a(n) = A000203(n) + 3*A078708(n). - R. J. Mathar, May 19 2020

Sum_{k=1..n} a(k) = (11*Pi^2/36) * n^2 + O(n*log(n)). - Amiram Eldar, Dec 16 2022

Extensions

Zero removed and offset corrected by Seiichi Manyama, Feb 28 2017