a(n) = Product_{k=1..n, gcd(n,k) = 1} prime(k).

Terms

a(0) =1a(1) =2a(2) =2a(3) =6a(4) =10a(5) =210a(6) =22a(7) =30030a(8) =1870a(9) =149226a(10) =3910a(11) =6469693230a(12) =11594a(14) =3215630a(15) =741422598a(16) =2569288370a(18) =28045886a(20) =19644868330