a(n) is smallest number which is uniquely a(j)+a(k).

Terms

a(0) =4a(1) =7a(2) =11a(3) =15a(4) =18a(5) =19a(6) =23a(7) =25a(8) =27a(9) =31a(10) =32a(11) =33a(12) =35a(13) =41a(14) =47a(15) =49a(16) =55a(17) =57a(18) =61a(19) =63a(20) =75a(21) =87a(22) =89a(23) =91a(24) =105a(25) =119a(26) =121a(27) =125a(28) =129a(29) =133