OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..25
FORMULA
a(n) = Sum_{d|n} phi(n/d)*(n*d)!/(d!^k*n^2) for n>0, a(0) = 1.
From Vaclav Kotesovec, Aug 23 2015: (Start)
a(n) ~ (n^2)! / (n^2 * (n!)^n).
a(n) ~ n^(n^2 - n/2 - 1) / (exp(1/12) * (2*Pi)^((n-1)/2)).
(End)
MAPLE
with(numtheory):
a:= n-> `if`(n=0, 1, add(phi(n/d)*(n*d)!/(d!^n*n^2), d=divisors(n))):
seq(a(n), n=0..10);
MATHEMATICA
a[n_] := If[n == 0, 1, DivisorSum[n, EulerPhi[n/#]*(n*#)!/(#!^n*n^2)&]];
Table[a[n], {n, 0, 10}] (* Jean-François Alcover, Mar 25 2017, translated from Maple *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Dec 21 2014
STATUS
approved