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

Terms

a(0) =1a(1) =6a(2) =46a(3) =47a(4) =48a(5) =49a(6) =50a(7) =51a(8) =52a(9) =53a(10) =54a(11) =406a(12) =416a(13) =426a(14) =436a(15) =446a(16) =456a(17) =466a(18) =476a(19) =486a(20) =3646a(21) =3655a(22) =3664a(23) =3673a(24) =3682a(25) =3691a(26) =3700a(27) =3709a(28) =3718a(29) =3728