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 A137121 #7 Apr 12 2024 09:51:27 %S A137121 6,66,74,76,666,744,6666,6734,6756,7574,57756,66666,66756,67434,67656, %T A137121 74474,74476,577734,666666,666756,667334,667566,667656,745356,745476, %U A137121 6666666,6666756,6667566,6667656,6674334,6734744,6756734,7373376,7453574,7465744,7466434,7533576,7574744,66666666,66666756,66667566,66667656,66673334 %N A137121 Numbers k such that k and k^2 use only the digits 3, 4, 5, 6 and 7. %C A137121 Generated with DrScheme. %H A137121 Jonathan Wellons, <a href="/A137121/b137121.txt">Table of n, a(n) for n = 1..224</a> %H A137121 J. Wellons, <a href="https://web.archive.org/web/20090206165028/http://jonathanwellons.com/shared-digits/">Tables of Shared Digits</a> [archived] %e A137121 757473746453656^2 = 573766476566537535636555766336. %K A137121 base,nonn %O A137121 1,1 %A A137121 Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008