a(n) = C(2n,n)*C(2n+2,n+1)/(n+2).

Terms

a(0) =1a(1) =4a(2) =30a(3) =280a(4) =2940a(5) =33264a(6) =396396a(7) =4907760a(8) =62573940a(9) =816621520a(10) =10861066216a(11) =146738321184