(s(n)+7)/10, where s(n)=n-th base 10 palindrome that starts with 3.

Terms

a(0) =1a(1) =4a(2) =31a(3) =32a(4) =33a(5) =34a(6) =35a(7) =36a(8) =37a(9) =38a(10) =39a(11) =40a(12) =301a(13) =312a(14) =323a(15) =334a(16) =345a(17) =356a(18) =367a(19) =378a(20) =389a(21) =400a(22) =3001a(23) =3011a(24) =3021a(25) =3031a(26) =3041a(27) =3051a(28) =3061a(29) =3071