Numbers with a single 3 in their base 4 expansion.

Terms

a(0) =3a(1) =7a(2) =11a(3) =12a(4) =13a(5) =14a(6) =19a(7) =23a(8) =27a(9) =28a(10) =29a(11) =30a(12) =35a(13) =39a(14) =43a(15) =44a(16) =45a(17) =46a(18) =48a(19) =49a(20) =50a(21) =52a(22) =53a(23) =54a(24) =56a(25) =57a(26) =58a(27) =67a(28) =71a(29) =75