a(n)=(s(n)+1)/4, where s(n)=n-th base 4 palindrome that starts with 3.

Terms

a(0) =1a(1) =4a(2) =13a(3) =14a(4) =15a(5) =16a(6) =49a(7) =54a(8) =59a(9) =64a(10) =193a(11) =197a(12) =201a(13) =205a(14) =210a(15) =214a(16) =218a(17) =222a(18) =227a(19) =231a(20) =235a(21) =239a(22) =244a(23) =248a(24) =252a(25) =256a(26) =769a(27) =789a(28) =809a(29) =829