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 A228774 #13 Sep 05 2013 05:57:08
%S A228774 10,11,12,13,14,15,170,171,172,173,174,175,186,187,188,189,190,191,
%T A228774 202,203,204,205,206,207,218,219,220,221,222,223,234,235,236,237,238,
%U A228774 239,250,251,252,253,254,255,2730,2731,2732,2733,2734,2735,2746,2747,2748
%N A228774 Numbers n such that the digits of n, once written in base 16, are only the hexadecimal digits A to F.
%H A228774 Charles R Greathouse IV, <a href="/A228774/b228774.txt">Table of n, a(n) for n = 0..10000</a>
%e A228774 2989 is BAD in base 16.
%t A228774 FromDigits[#, 16]& /@ Flatten[Table[Tuples[Range[10, 15], k], {k, 1, 3}], 1]
%t A228774 Select[Range[3000], Min[IntegerDigits[#, 16]] > 9 &] (* _T. D. Noe_, Sep 04 2013 *)
%o A228774 (PARI) a(n)=my(d);while(n>=6^(d+1),n-=6^d++);sum(i=0,d,((n\6^i)%6+10)<<(4*i)) \\ _Charles R Greathouse IV_, Sep 04 2013
%Y A228774 Cf. A055645, A132675, A132676, A140969, A187829.
%K A228774 nonn,base,easy
%O A228774 0,1
%A A228774 _Jean-François Alcover_, Sep 04 2013