OFFSET
0,4
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..575
Wikipedia, Partition of a set
FORMULA
EXAMPLE
a(3) = 3 = 1 + 1 + 0 + 1 + 0 : 123, 12|3, 13|2, 1|23, 1|2|3.
MAPLE
b:= proc(n, x, y, m) option remember; `if`(n=0, m,
`if`(x+m>0, b(n-1, y, x, m)*(x+m), 0)+b(n-1, y, x+1, m)+
`if`(y>0, b(n-1, y-1, x, m+1)*y, 0))
end:
a:= n-> b(n, 0$3):
seq(a(n), n=0..25);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jun 05 2023
STATUS
approved