a(n) is smallest number != a(j) + a(k), j < k and a(1) = 1, a(2) = 6.

Terms

a(0) =1a(1) =6a(2) =8a(3) =10a(4) =12a(5) =15a(6) =17a(7) =19a(8) =24a(9) =26a(10) =28a(11) =33a(12) =35a(13) =37a(14) =42a(15) =44a(16) =46a(17) =51a(18) =53a(19) =55a(20) =60a(21) =62a(22) =64a(23) =69a(24) =71a(25) =73a(26) =78a(27) =80a(28) =82a(29) =87