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 A180408 #11 Mar 24 2014 02:29:16
%S A180408 123456789,23456789,13456789,12456789,12356789,12346789,12345789,
%T A180408 12345689,12345679,12345678,23456789,23456789,3456789,2456789,2356789,
%U A180408 2346789,2345789,2345689,2345679,2345678,13456789,3456789,13456789,1456789,1356789,1346789,1345789
%N A180408 Nonzero digits not used in n.
%F A180408 a(n) = 123456789 after removing any digits that appear in n. If n uses all digits, then a(n) = 0.
%e A180408 a(13) = 123456789 without 1 and 3 = 2456789.
%e A180408 a(123456789) = 0 (by definition).
%t A180408 newn[n_]:=FromDigits[Complement[Range[9],IntegerDigits[n]]]; Table[newn[i],{i,50}] (* _Harvey P. Dale_, Nov 21 2010 *)
%K A180408 easy,nonn,base
%O A180408 0,1
%A A180408 _Dominick Cancilla_, Sep 02 2010
%E A180408 More terms from _Harvey P. Dale_, Nov 21 2010