OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..800
EXAMPLE
a(2) = 3: 2ab, 2ba, 1a1b.
a(3) = 18: 3aab, 3aba, 3baa, 3abb, 3bab, 3bba, 2aa1b, 2ab1a, 2ba1a, 2ab1b, 2ba1b, 2bb1a, 1a2ab, 1a2ba, 1a2bb, 1b2aa, 1b2ab, 1b2ba.
MAPLE
b:= proc(n, i, k, p) option remember;
`if`(n=0, p!, `if`(i<1, 0, add(binomial(k^i, j)*
b(n-i*j, min(n-i*j, i-1), k, p+j)/j!, j=0..n/i)))
end:
a:= n-> (k-> add(b(n$2, i, 0)*(-1)^(k-i)*binomial(k, i), i=0..k))(2):
seq(a(n), n=0..27);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 24 2019
STATUS
approved