OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
Multiplicative with a(p^e) = 4*e+1.
a(n) = Sum_{d|n} 4^omega(d).
G.f.: Sum_{k>=1} 4^omega(k) * x^k/(1 - x^k).
Dirichlet g.f.: zeta(s)^2 * Product_{primes p} (1 + 3/p^s). - Vaclav Kotesovec, May 15 2021
Dirichlet g.f.: zeta(s)^5 * Product_{primes p} (1 - 6/p^(2*s) + 8/p^(3*s) - 3/p^(4*s)). - Vaclav Kotesovec, Aug 20 2021
MATHEMATICA
Table[DivisorSigma[0, n^4], {n, 1, 100}] (* Amiram Eldar, May 15 2021 *)
PROG
(PARI) a(n) = numdiv(n^4);
(PARI) a(n) = prod(k=1, #f=factor(n)[, 2], 4*f[k]+1);
(PARI) a(n) = sumdiv(n, d, 4^omega(d));
(PARI) my(N=99, x='x+O('x^N)); Vec(sum(k=1, N, 4^omega(k)*x^k/(1-x^k)))
(PARI) for(n=1, 100, print1(direuler(p=2, n, (1 + 3*X)/(1 - X)^2)[n], ", ")) \\ Vaclav Kotesovec, May 15 2021
(PARI) for(n=1, 100, print1(direuler(p=2, n, (1 - 6*X^2 + 8*X^3 - 3*X^4)/(1 - X)^5)[n], ", ")) \\ Vaclav Kotesovec, Aug 20 2021
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Seiichi Manyama, May 15 2021
STATUS
approved