a(n) = 2^n * (2*n)! / (n!)^2.

Terms

a(0) =1a(1) =4a(2) =24a(3) =160a(4) =1120a(5) =8064a(6) =59136a(7) =439296a(8) =3294720a(9) =24893440a(10) =189190144a(11) =1444724736a(12) =11076222976a(13) =85201715200a(14) =657270374400