OFFSET
0,5
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..470
Wikipedia, Permutation
EXAMPLE
a(5) = 15 = 5*3: (1)(23)(45), (1)(24)(35), (1)(25)(34), ..., (1,2)(3,4)(5),
(1,3)(2,4)(5), (1,4)(2,3)(5).
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
add(`if`(j=0 or j=i, b(n-i*j, i-1)*(i-1)!^j/j!*
combinat[multinomial](n, i$j, n-i*j), 0), j=0..n/i)))
end:
a:= n-> b(n$2):
seq(a(n), n=0..35);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jul 04 2024
STATUS
approved