A354848 a(n) = (n-1)! * Sum_{d|n} d^(n/d + 1).
1, 5, 20, 150, 624, 9600, 36000, 811440, 6572160, 105235200, 442713600, 39437798400, 81430272000, 4956708556800, 137741700096000, 3014189418240000, 6067609067520000, 1977977787641856000, 2317659281473536000, 1297953221362237440000
Offset: 1
Keywords
Programs
-
Mathematica
a[n_] := (n - 1)! * DivisorSum[n, #^(n/# + 1) &]; Array[a, 20] (* Amiram Eldar, Jun 08 2022 *)
-
PARI
a(n) = (n-1)!*sumdiv(n, d, d^(n/d+1));
-
PARI
my(N=30, x='x+O('x^N)); Vec(serlaplace(-sum(k=1, N, log(1-k*x^k))))
Formula
a(n) = (n-1)! * A078308(n).
E.g.f.: -Sum_{k>0} log(1 - k * x^k).
If p is prime, a(p) = (p-1)! + p * p!.