A022431 a(n) = c(n-1) + c(n-3) where c is the sequence of numbers not in a.

1, 2, 7, 8, 10, 14, 17, 21, 24, 27, 29, 33, 35, 38, 41, 43, 47, 49, 53, 56, 59, 62, 65, 68, 71, 75, 77, 81, 84, 87, 90, 93, 96, 99, 102, 105, 107, 111, 113, 117, 119, 123, 125, 129, 131, 135