OFFSET
0,2
COMMENTS
Also matrices with four rows of nonnegative integers with distinct positive column sums and total element sum n.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..5000
MAPLE
b:= proc(n, i, p) option remember;
`if`(i*(i+1)/2<n, 0, `if`(n=0, p!, b(n, i-1, p)+
`if`(i>n, 0, b(n-i, i-1, p+1)*binomial(i+3, 3))))
end:
a:= n-> b(n$2, 0):
seq(a(n), n=0..40);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 03 2015
STATUS
approved