a(n)=(s(n)+2)/5, where s(n)=n-th base 5 palindrome that starts with 3.

Terms

a(0) =1a(1) =4a(2) =16a(3) =17a(4) =18a(5) =19a(6) =20a(7) =76a(8) =82a(9) =88a(10) =94a(11) =100a(12) =376a(13) =381a(14) =386a(15) =391a(16) =396a(17) =402a(18) =407a(19) =412a(20) =417a(21) =422a(22) =428a(23) =433a(24) =438a(25) =443a(26) =448a(27) =454a(28) =459a(29) =464