Numbers with a single 1 in their base 4 expansion.

Terms

a(0) =1a(1) =4a(2) =6a(3) =7a(4) =9a(5) =13a(6) =16a(7) =18a(8) =19a(9) =24a(10) =26a(11) =27a(12) =28a(13) =30a(14) =31a(15) =33a(16) =36a(17) =38a(18) =39a(19) =41a(20) =45a(21) =49a(22) =52a(23) =54a(24) =55a(25) =57a(26) =61a(27) =64a(28) =66a(29) =67