a(1)=1, a(n) = p*a(n-1), where p is the smallest prime satisfying gcd(n,p)=1.

Terms

a(0) =1a(1) =3a(2) =6a(3) =18a(4) =36a(5) =180a(6) =360a(7) =1080a(8) =2160a(9) =6480a(10) =12960a(11) =64800a(12) =129600a(13) =388800a(14) =777600a(15) =2332800a(16) =4665600a(17) =23328000a(18) =46656000a(19) =139968000a(20) =279936000a(21) =839808000a(22) =1679616000a(23) =8398080000a(24) =16796160000a(25) =50388480000a(26) =100776960000