a(n)=(s(n)+7)/9, where s(n)=n-th base 9 palindrome that starts with 2.

Terms

a(0) =1a(1) =3a(2) =19a(3) =20a(4) =21a(5) =22a(6) =23a(7) =24a(8) =25a(9) =26a(10) =27a(11) =163a(12) =173a(13) =183a(14) =193a(15) =203a(16) =213a(17) =223a(18) =233a(19) =243a(20) =1459a(21) =1468a(22) =1477a(23) =1486a(24) =1495a(25) =1504a(26) =1513a(27) =1522a(28) =1531a(29) =1541