a(n) = n!/gcd(n,3).

Terms

a(0) =1a(1) =2a(2) =2a(3) =24a(4) =120a(5) =240a(6) =5040a(7) =40320a(8) =120960a(9) =3628800a(10) =39916800a(11) =159667200a(12) =6227020800a(13) =87178291200a(14) =435891456000