a(n+1) is the smallest number not of the form a(i), a(i) + a(n-1), or |a(i) - a(n-1)|.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =10a(5) =5a(6) =8a(7) =11a(8) =14a(9) =17a(10) =20a(11) =23a(12) =26a(13) =13a(14) =16a(15) =19a(16) =22a(17) =25a(18) =28a(19) =31a(20) =34a(21) =37a(22) =40a(23) =43a(24) =46a(25) =49a(26) =52a(27) =55a(28) =58a(29) =29