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 A136831 #9 Apr 12 2024 09:51:26
%S A136831 0,1,10,11,100,101,110,1000,1001,1010,1011,1100,1101,10000,10001,
%T A136831 10010,10011,10100,10110,11000,11001,11010,100000,100001,100010,
%U A136831 100011,100100,100101,100110,101000,101001,101100,110000,110001,110010,110100,1000000,1000001,1000010,1000011,1000100,1000101,1000110,1001000,1001010,1001100,1010000
%N A136831 Numbers k such that k and k^2 use only the digits 0, 1, 2 and 7.
%C A136831 Generated with DrScheme.
%H A136831 Jonathan Wellons, <a href="/A136831/b136831.txt">Table of n, a(n) for n = 1..1361</a>
%H A136831 J. Wellons, <a href="https://web.archive.org/web/20090206165028/http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a> [archived]
%e A136831 110100010001011^2 = 12122012202222722220221022121.
%t A136831 With[{c={0,1,2,7}},Select[FromDigits/@Tuples[c,7],SubsetQ[ c,IntegerDigits[ #^2]]&]] (* _Harvey P. Dale_, Dec 21 2014 *)
%K A136831 base,nonn
%O A136831 1,3
%A A136831 Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008