a(n) = lcm(1,...,2n+2)/2.

Terms

a(0) =1a(1) =6a(2) =30a(3) =420a(4) =1260a(5) =13860a(6) =180180a(7) =360360a(8) =6126120a(9) =116396280a(10) =116396280a(11) =2677114440a(12) =13385572200a(13) =40156716600