OFFSET
1,2
FORMULA
a(n) = Sum_{k=0..n} (-1)^(n-k) * binomial(n,k) * sigma_{2*k}(n).
MATHEMATICA
a[n_]:= Sum[(-1)^(n-k)*Binomial[n, k]*DivisorSigma[2*k, n], {k, 0, n}]; Array[a, 14] (* Stefano Spezia, Nov 22 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d^2-1)^n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 22 2023
STATUS
approved