OFFSET
1,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = (sigma_13(n) - 11*sigma_9(n) + 10*sigma_3(n))/2640.
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 *)
PROG
(PARI) a(n) = sum(k=1, n-1, sigma(k, 3)*sigma(n-k, 9)) \\ Felix Fröhlich, Dec 23 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 23 2016
STATUS
approved