a(n) = (n-1)! * (n+1)!.A175430a(n) = (n-1)! * (n+1)!.Terms a(0) =2a(1) =6a(2) =48a(3) =720a(4) =17280a(5) =604800a(6) =29030400a(7) =1828915200a(8) =146313216000External referencesoeis: A175430