A081861 a(n) = (1/24)*(sigma_3(2*n-1) - sigma_1(2*n-1)).

0, 1, 5, 14, 31, 55, 91, 146, 204, 285, 400, 506, 655, 850, 1015, 1240, 1552, 1804, 2109, 2562, 2870, 3311, 3971, 4324, 4914, 5730, 6201, 6990, 8000, 8555, 9455, 10846, 11536, 12529, 14192, 14910, 16206, 18371, 19088, 20540, 22990, 23821, 25794

Offset: 1

Author

Benoit Cloitre, Apr 11 2003

Keywords

• nonn
• easy

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000203, A001158, A008438, A045823, A081863(1).

Programs

Mathematica

Table[(DivisorSigma[3,2n-1]-DivisorSigma[1,2n-1])/24,{n,50}] (* Harvey P. Dale, Dec 15 2012 *)

PARI

a(n) = my(f = factor(2*n-1)); (sigma(f, 3) - sigma(f)) / 24; \\ Amiram Eldar, Jan 04 2025

Formula

a(n) = (A045823(n-1) - A008438(n-1)) / 24. - Amiram Eldar, Jan 04 2025