OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..250
FORMULA
a(n) = A291680(2n,n).
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-> `if`(n=0, 1, b(0, 2*n, n)-b(0, 2*n, n-1)):
seq(a(n), n=0..20);
MATHEMATICA
b[u_, o_, k_] := b[u, o, k] = If[u + o == 0, 1,
Sum[b[u - j, o + j - 1, k], {j, 1, Min[2, u]}] +
Sum[b[u + j - 1, o - j, k], {j, 1, Min[k, o]}]];
a[n_] := If[n == 0, 1, b[0, 2*n, n] - b[0, 2*n, n - 1]];
Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Apr 21 2022, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 27 2018
STATUS
approved