A356543 - OEIS

A356543

a(n) = Sum_{d|n} (d!)^(n/d-1).

1, 2, 2, 4, 2, 12, 2, 34, 38, 138, 2, 1546, 2, 5106, 15698, 54274, 2, 889314, 2, 5689090, 25448258, 39917826, 2, 2486196610, 207360002, 6227024898, 131683574018, 215393466370, 2, 14769495662082, 2, 86475697160194, 1593350982706178, 355687428161538, 648227266560002

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..35.

FORMULA

G.f.: Sum_{k>=1} x^k/(1 - k! * x^k).

If p is prime, a(p) = 2.

MATHEMATICA

a[n_] := DivisorSum[n, (#)!^(n/# - 1) &]; Array[a, 35] (* Amiram Eldar, Aug 30 2023 *)

PROG

(PARI) a(n) = sumdiv(n, d, d!^(n/d-1));