OFFSET
1,2
COMMENTS
The next term (a(6)) has 169 digits. - Harvey P. Dale, Sep 08 2020
FORMULA
L.g.f.: -log(Product_{k>=1} (1 - x^k)^(k^(k^3-1))) = Sum_{k>=1} a(k)*x^k/k.
MATHEMATICA
Table[Total[Divisors[n]^Divisors[n]^3], {n, 5}] (* Harvey P. Dale, Sep 08 2020 *)
a[n_] := DivisorSum[n, #^(#^3) &]; Array[a, 5] (* Amiram Eldar, May 11 2021 *)
PROG
(PARI) {a(n) = sumdiv(n, d, d^d^3)}
(PARI) N=10; x='x+O('x^N); Vec(x*deriv(-log(prod(k=1, N, (1-x^k)^(k^(k^3-1))))))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 16 2019
STATUS
approved