a(n)=(s(n)+5)/9, where s(n)=n-th base 9 palindrome that starts with 4.

Terms

a(0) =1a(1) =5a(2) =37a(3) =38a(4) =39a(5) =40a(6) =41a(7) =42a(8) =43a(9) =44a(10) =45a(11) =325a(12) =335a(13) =345a(14) =355a(15) =365a(16) =375a(17) =385a(18) =395a(19) =405a(20) =2917a(21) =2926a(22) =2935a(23) =2944a(24) =2953a(25) =2962a(26) =2971a(27) =2980a(28) =2989a(29) =2999