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 A136904 #15 Jul 03 2025 10:04:50
%S A136904 0,2,8,20,22,68,80,200,202,220,262,668,680,800,2000,2002,2020,2022,
%T A136904 2200,2202,2620,6668,6680,6800,8000,8262,20000,20002,20020,20022,
%U A136904 20200,20220,20602,22000,22002,22020,24622,26200,66668,66680,66800,68000,80000,82620,200000,200002,200020,200022,200200,200202,200220,202000,202002,202200,206020
%N A136904 Numbers k such that k and k^2 use only the digits 0, 2, 4, 6 and 8.
%C A136904 Generated with DrScheme.
%C A136904 Subsequence of A014263. - _Michel Marcus_, Oct 04 2013
%H A136904 Jonathan Wellons, <a href="/A136904/b136904.txt">Table of n, a(n) for n = 1..1038</a>
%H A136904 J. Wellons, <a href="https://web.archive.org/web/20090206165028/http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a> [archived]
%e A136904 828268460602^2 = 686028642828006826202404.
%t A136904 Select[Range[0,206050],AllTrue[Join[IntegerDigits[#],IntegerDigits[#^2]],EvenQ] &] (* _Stefano Spezia_, Jul 03 2025 *)
%o A136904 (PARI) evdigs(n) = {if (n==0, return (1)); digs = digits(n); for (i = 1, #digs, if (digs[i] % 2, return (0));); return (1);}
%o A136904 isok(n) = evdigs(n) && evdigs(n^2); \\ _Michel Marcus_, Oct 04 2013
%Y A136904 Cf. A014263.
%K A136904 base,nonn
%O A136904 1,2
%A A136904 Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008