a(n) = LCM(1,2, ..., 2n+1)/6.

Terms

a(0) =1a(1) =10a(2) =70a(3) =420a(4) =4620a(5) =60060a(6) =60060a(7) =2042040a(8) =38798760a(9) =38798760a(10) =892371480a(11) =4461857400a(12) =13385572200a(13) =388181593800