A363647 Expansion of Sum_{k>0} (1/(1 - (k*x)^k)^3 - 1).
3, 18, 91, 879, 9396, 145010, 2470665, 50728749, 1162458352, 30058615320, 855935011911, 26761537897338, 908625319776864, 33340089815701086, 1313681976619686558, 55341921135416377497, 2481720785659010292702, 118040125809311823596960
Offset: 1
Keywords
Programs
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Mathematica
a[n_] := DivisorSum[n, (n/#)^n * Binomial[# + 2, 2] &]; Array[a, 20] (* Amiram Eldar, Jul 17 2023 *)
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PARI
a(n) = sumdiv(n, d, (n/d)^n*binomial(d+2, 2));
Formula
a(n) = Sum_{d|n} (n/d)^n * binomial(d+2,2).