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

Terms

a(0) =1a(1) =4a(2) =5a(3) =6a(4) =7a(5) =8a(6) =9a(7) =10a(8) =11a(9) =12a(10) =13a(11) =14a(12) =15a(13) =17a(14) =18a(15) =19a(16) =21a(17) =22a(18) =23a(19) =26a(20) =27a(21) =29a(22) =31a(23) =33a(24) =34a(25) =37a(26) =38a(27) =39a(28) =41a(29) =43