OFFSET
1,2
FORMULA
E.g.f.: Sum_{k>0} log(1-x^k)/(x^k-1). - Vladeta Jovovic, Aug 01 2004
EXAMPLE
a(6) = 6! *(1 + (1 + 1/2) + (1 + 1/2 + 1/3) + (1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6)) because 1, 2, 3 and 6 are the divisors of 6.
MATHEMATICA
a[n_] := n! * DivisorSum[n, HarmonicNumber[#] &]; Array[a, 20] (* Amiram Eldar, Aug 18 2023 *)
PROG
(PARI) a(n) = n!*sumdiv(n, k, sum(j=1, k, 1/j)); \\ Michel Marcus, Aug 20 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Feb 05 2002
EXTENSIONS
a(20)-a(22) from Amiram Eldar, Aug 18 2023
STATUS
approved