a(n) = Product_{i=2..n} phi(i)/bigomega(i).

Terms

a(0) =1a(1) =2a(2) =2a(3) =8a(4) =8a(5) =48a(6) =64a(7) =192a(8) =384a(9) =3840a(10) =5120a(11) =61440a(12) =184320a(13) =737280a(14) =1474560a(15) =23592960a(16) =47185920a(17) =849346560a(18) =2264924160a(19) =13589544960a(20) =67947724800