a(n) = Sum_{k=0..n} C(n+k,n-k)*C(2*n-k,k).

Terms

a(0) =1a(1) =2a(2) =11a(3) =62a(4) =367a(5) =2232a(6) =13820a(7) =86662a(8) =548591a(9) =3498146a(10) =22436251a(11) =144583496a(12) =935394436a(13) =6071718512a(14) =39523955552a(15) =257913792342