a(n) = Sum_{k=0..n} binomial(4*n-4,k).

Terms

a(0) =1a(1) =1a(2) =11a(3) =93a(4) =794a(5) =6885a(6) =60460a(7) =536155a(8) =4791323a(9) =43081973a(10) =389329652a(11) =3533047572a(12) =32174057272a(13) =293874981603