OFFSET
1,3
REFERENCES
Jean-Pierre Serre, A Course in Arithmetic, Springer-Verlag, 1973, Chapter VII, Section 4.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = (11*sigma_9(n)-21*sigma_5(n)+10*sigma_3(n))/5040.
MATHEMATICA
Table[Sum[If[k == 0, 0, DivisorSigma[3, k]] DivisorSigma[5, n - k], {k, 0, n - 1}], {n, 28}] (* Michael De Vlieger, Dec 22 2016 *)
a[n_] := (11 * DivisorSigma[9, n] - 21 * DivisorSigma[5, n] + 10 * DivisorSigma[3, n]) / 5040; Array[a, 30] (* Amiram Eldar, Jan 07 2025 *)
PROG
(PARI) a(n) = {my(f = factor(n)); (11 * sigma(f, 9) - 21 * sigma(f, 5) + 10 * sigma(f, 3)) / 5040; } \\ Amiram Eldar, Jan 07 2025
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 22 2016
STATUS
approved