a(n) = 3*binomial(4*n,n)/(4*n-1).

Terms

a(0) =4a(1) =12a(2) =60a(3) =364a(4) =2448a(5) =17556a(6) =131560a(7) =1017900a(8) =8069424a(9) =65204656a(10) =535070172a(11) =4446927732a(12) =37353738800a(13) =316621743480