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

Terms

a(0) =2a(1) =4a(2) =5a(3) =7a(4) =9a(5) =10a(6) =11a(7) =13a(8) =14a(9) =15a(10) =17a(11) =19a(12) =21a(13) =22a(14) =23a(15) =25a(16) =27a(17) =29a(18) =30a(19) =31a(20) =35a(21) =37a(22) =39a(23) =41a(24) =45a(25) =46a(26) =47a(27) =49a(28) =51a(29) =55