A363648 Expansion of Sum_{k>0} (1/(1 - (k*x)^k)^4 - 1).
4, 26, 128, 1219, 12556, 195278, 3294292, 67773349, 1550075836, 40097713880, 1141246682808, 35686524105658, 1211500426369572, 44454809534927314, 1751576172678539608, 73789791194939982793, 3308961047545347057848, 157387135278770854655312
Offset: 1
Keywords
Programs
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Mathematica
a[n_] := DivisorSum[n, (n/#)^n * Binomial[# + 3, 3] &]; Array[a, 20] (* Amiram Eldar, Jul 17 2023 *)
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PARI
a(n) = sumdiv(n, d, (n/d)^n*binomial(d+3, 3));
Formula
a(n) = Sum_{d|n} (n/d)^n * binomial(d+3,3).