a(n) = (4/(n + 1)) * C(5*n, n).

Terms

a(0) =4a(1) =10a(2) =60a(3) =455a(4) =3876a(5) =35420a(6) =339300a(7) =3362260a(8) =34179860a(9) =354465254a(10) =3735373880a(11) =39884521950a(12) =430571952300