a(1)=1; for n>1, a(n) = a(n-1) + lcm(a(n-1),n).

Terms

a(0) =1a(1) =3a(2) =6a(3) =18a(4) =108a(5) =216a(6) =1728a(7) =3456a(8) =6912a(9) =41472a(10) =497664a(11) =995328a(12) =13934592a(13) =27869184a(14) =167215104a(15) =334430208a(16) =6019743744a(17) =12039487488a(18) =240789749760a(19) =481579499520a(20) =963158999040