a(n) = binomial(4*n + 2,n).

Terms

a(0) =1a(1) =6a(2) =45a(3) =364a(4) =3060a(5) =26334a(6) =230230a(7) =2035800a(8) =18156204a(9) =163011640a(10) =1471442973a(11) =13340783196a(12) =121399651100