a(n) = c(n) + c(n-1) where c is the sequence of numbers not in a.

Terms

a(0) =2a(1) =4a(2) =8a(3) =11a(4) =13a(5) =16a(6) =19a(7) =22a(8) =26a(9) =29a(10) =32a(11) =35a(12) =38a(13) =41a(14) =44a(15) =47a(16) =49a(17) =52a(18) =55a(19) =58a(20) =61a(21) =64a(22) =67a(23) =70a(24) =73a(25) =76a(26) =79a(27) =82a(28) =85a(29) =88