a(n) = least positive integer > a(n-1) and not a(i)*a(j) for 1<=i<j<=n, with initial terms 3,4.

Terms

a(0) =3a(1) =4a(2) =5a(3) =6a(4) =7a(5) =8a(6) =9a(7) =10a(8) =11a(9) =13a(10) =14a(11) =16a(12) =17a(13) =19a(14) =22a(15) =23a(16) =25a(17) =26a(18) =29a(19) =31a(20) =34a(21) =37a(22) =38a(23) =41a(24) =43a(25) =46a(26) =47a(27) =49a(28) =53a(29) =58