OFFSET
0,4
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..450
FORMULA
EXAMPLE
a(4) = 9: (1,2)(3,4), (1,3)(2,4), (1,4)(2,3), (2,3,4,1), (2,4,1,3), (3,1,4,2), (3,4,2,1), (4,1,2,3), (4,3,1,2).
MAPLE
a:= n-> `if`(n=0, 1, add(n!/d!*(d/n)^d, d=numtheory[divisors](n) minus {n})):
seq(a(n), n=0..23); # Alois P. Heinz, Apr 20 2021
PROG
(PARI) a(n) = if (n, sumdiv(n, d, if (d<n, (n!/d!)*(d/n)^d)), 1); \\ Michel Marcus, Apr 21 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Gary Yane, Apr 20 2021
STATUS
approved