OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1663
Wikipedia, Partition of a set
FORMULA
EXAMPLE
a(0) = 1: {}|{}|{}.
a(1) = 1: 1|2|3.
a(2) = 7: 12|34|56, 12|35|46, 12|36|45, 13|24|56, 14|23|56, 15|26|34, 16|25|34.
MAPLE
a:= n-> `if`(n=0, 1, 3*binomial(2*n-1, n)-2):
seq(a(n), n=0..27);
# second Maple program:
a:= proc(n) option remember; `if`(n<3, 3*n*(n-1)+1, ((15*n^2
-31*n+12)*a(n-1)-(3*n-2)*(4*n-6)*a(n-2))/((3*n-5)*n))
end:
seq(a(n), n=0..27);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Feb 19 2024
STATUS
approved