A279926 a(n) = Sum_{k=1..n-1} sigma_3(k)*sigma_9(n-k).

0, 1, 522, 24329, 454250, 4905766, 36532244, 207705929, 961214238, 3784166376, 13066960126, 40511160326, 114681233758, 300599979884, 737035375772, 1705830324553, 3751239987240, 7887626314003, 15927815870322, 31031953887704, 58508991327728, 107133058597170

Offset: 1

Author

Seiichi Manyama, Dec 23 2016

Keywords

• nonn

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A001158, A013957, A013961, A279888, A279917.

Programs

Mathematica

Table[Sum[If[k == 0, 0, DivisorSigma[3, k]] DivisorSigma[9, n - k], {k, 0, n - 1}], {n, 22}] (* Michael De Vlieger, Dec 23 2016 *)

PARI

a(n) = sum(k=1, n-1, sigma(k, 3)*sigma(n-k, 9)) \\ Felix Fröhlich, Dec 23 2016

Formula

a(n) = (sigma_13(n) - 11*sigma_9(n) + 10*sigma_3(n))/2640.