a(n) = least positive integer > a(n-1) and not a(i)*a(j) for 1<=i<=j<=n, n >= 2.

Terms

a(0) =2a(1) =4a(2) =5a(3) =6a(4) =7a(5) =9a(6) =11a(7) =13a(8) =15a(9) =17a(10) =19a(11) =21a(12) =23a(13) =27a(14) =29a(15) =31a(16) =32a(17) =33a(18) =37a(19) =39a(20) =40a(21) =41a(22) =43a(23) =47a(24) =48a(25) =50a(26) =51a(27) =53a(28) =56a(29) =57