a(n) = n! * Sum_{k=0..n} (2*k)! / (k!)^3.

Terms

a(0) =1a(1) =3a(2) =12a(3) =56a(4) =294a(5) =1722a(6) =11256a(7) =82224a(8) =670662a(9) =6084578a(10) =61030536a(11) =672041328a(12) =8067200092a(13) =104884001796