A022427 a(n) = c(n-1) + c(n-3) where c is the sequence of numbers not in a.

1, 2, 3, 10, 12, 14, 16, 19, 22, 26, 30, 33, 37, 39, 43, 45, 48, 51, 53, 56, 59, 61, 65, 67, 70, 73, 76, 79, 82, 85, 88, 91, 95, 97, 101, 104, 107, 111, 113, 117, 120, 123, 126, 129, 132, 135, 139, 141, 145, 147, 151, 153, 157, 159, 163, 165, 169, 171