OFFSET
9,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 9..1000
MAPLE
b:= proc(u, o, k) option remember; `if`(u+o=0, 1,
add(b(u-j, o+j-1, k), j=1..min(2, u))+
add(b(u+j-1, o-j, k), j=1..min(k, o)))
end:
a:= n-> (k-> b(0, n, k)-b(0, n, k-1))(9):
seq(a(n), n=9..30);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 27 2018
STATUS
approved