a(n) = lcm(a(n-1), n) - gcd(a(n-1), n) where a(1) = 1.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =9a(5) =15a(6) =104a(7) =96a(8) =285a(9) =565a(10) =6214a(11) =37282a(12) =484665a(13) =6785309a(14) =101779634a(15) =814237070a(16) =13842030189a(17) =83052181131