This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A030285 #8 Aug 24 2012 10:47:39
%S A030285 0,1,2,3,4,5,6,7,8,9,11,22,33,44,55,66,77,88,99,101,222,303,414,505,
%T A030285 616,707,818,909,1111,2002,3113,4004,5115,6006,7117,8008,9119,20002,
%U A030285 31113,40004,51115,60006,71117,80008,91119,200002,311113,400004
%N A030285 Palindromes whose digits do not appear in previous term.
%C A030285 Although the sequence is infinite, in a sense it cycles. The outside of the next palindrome beginning with 20 continues 31, 40, 51, 60, 71, 80, 91 and back to 20. The inside oscillates between increasing number of zeros and ones.
%t A030285 NextPalindrome[n_] := Block[{l = Floor[Log[10, n] + 1], idn = IntegerDigits[n]}, If[ Union[idn] == {9}, Return[n + 2], If[l < 2, Return[n + 1], If[ FromDigits[ Reverse[ Take[idn, Ceiling[l/2]]]] FromDigits[ Take[idn, -Ceiling[l/2]]], FromDigits[ Join[ Take[idn, Ceiling[l/2]], Reverse[ Take[idn, Floor[l/2]]]]], idfhn = FromDigits[ Take[idn, Ceiling[l/2]]] + 1; idp = FromDigits[ Join[ IntegerDigits[idfhn], Drop[ Reverse[ IntegerDigits[idfhn]], Mod[l, 2]]]]]]]]; a[0] = 0; a[n_] := a[n] = Block[{k = a[n - 1], d = IntegerDigits[a[n - 1]]}, While[ Intersection[d, IntegerDigits[k]] != {}, k = NextPalindrome[k]]; k]; Table[ a[n], {n, 0, 50}]
%K A030285 nonn,base
%O A030285 1,3
%A A030285 _Patrick De Geest_
%E A030285 Edited by _Robert G. Wilson v_, Jun 27 2003