OFFSET
1,1
COMMENTS
In general, for k>=1, Sum_{j=1..n} sigma(j*k) ~ A069097(k) * Pi^2 * n^2 / (12*k). - Vaclav Kotesovec, May 11 2024
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A000203(9*n).
Sum_{k=1..n} a(k) = (35*Pi^2/36) * n^2 + O(n*log(n)). - Amiram Eldar, Dec 16 2022
MATHEMATICA
Table[DivisorSigma[1, 9 n], {n, 50}] (* Michael De Vlieger, Mar 01 2017 *)
PROG
(PARI) a(n) = sigma(9*n) \\ Amiram Eldar, Dec 16 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 01 2017
STATUS
approved