a(n) = Product_{i=3..n} (prime(i) - 4).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =21a(5) =189a(6) =2457a(7) =36855a(8) =700245a(9) =17506125a(10) =472665375a(11) =15597957375a(12) =577124422875