OFFSET
1,1
COMMENTS
In general, for p prime, Sum_{j=1..n} tau(j*p) ~ (2*p - 1) * n * (log(n) - 1 + 2*gamma)/p + n*log(p)/p, where gamma is the Euler-Mascheroni constant A001620.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
FORMULA
Sum_{k=1..n} a(k) ~ n * (5*(log(n) + 2*gamma - 1) + log(3)) / 3, where gamma is the Euler-Mascheroni constant A001620.
MATHEMATICA
Table[DivisorSigma[0, 3*n], {n, 1, 150}]
PROG
(PARI) a(n) = numdiv(3*n); \\ Michel Marcus, May 20 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, May 11 2024
STATUS
approved