a(1)=2; thereafter a(n) = a(n-1) + gpf(a(n-1)) - 1, where gpf = greatest prime factor = A006530.

Terms

a(0) =2a(1) =3a(2) =5a(3) =9a(4) =11a(5) =21a(6) =27a(7) =29a(8) =57a(9) =75a(10) =79a(11) =157a(12) =313a(13) =625a(14) =629a(15) =665a(16) =683a(17) =1365a(18) =1377a(19) =1393a(20) =1591a(21) =1633a(22) =1703a(23) =1833a(24) =1879a(25) =3757a(26) =3773a(27) =3783a(28) =3879a(29) =4309