a(1) = 1, a(n) = a(n-1) times smallest prime factor of n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =12a(4) =60a(5) =120a(6) =840a(7) =1680a(8) =5040a(9) =10080a(10) =110880a(11) =221760a(12) =2882880a(13) =5765760a(14) =17297280a(15) =34594560a(16) =588107520a(17) =1176215040a(18) =22348085760a(19) =44696171520a(20) =134088514560a(21) =268177029120