A081866 a(n) = sigma_9(2n-1).

1, 19684, 1953126, 40353608, 387440173, 2357947692, 10604499374, 38445332184, 118587876498, 322687697780, 794320419872, 1801152661464, 3814699218751, 7625984925160, 14507145975870, 26439622160672, 46413842369328, 78815680978608, 129961739795078, 208738965677816

Offset: 1

Author

Benoit Cloitre, Apr 12 2003

Keywords

• nonn

Links

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

Crossrefs

Cf. A013957.

Programs

Mathematica

DivisorSigma[9,Range[1,41,2]] (* Harvey P. Dale, Dec 01 2013 *)

PARI

a(n) = sigma(2*n-1, 9); \\ Amiram Eldar, Jan 08 2025

Formula

Sum_{k=1..n} a(k) ~ c * n^10, where c = 31 * Pi^10 / 56700 = 51.200872... . - Amiram Eldar, Jan 08 2025