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 A036511 #12 Jul 27 2018 08:46:56
%S A036511 4,144,1444,44944,6441444,47444544,4434494464,44424414441,
%T A036511 4243443441444,44844344414464,444431244445444,44044624434444544,
%U A036511 441544444344443449,14444545446449449444,346454444084444444644,44024844440444424044544,444448493447444044441744
%N A036511 Smallest square containing exactly n 4's.
%C A036511 a(21) > 10^28. - _Giovanni Resta_, Jul 27 2018
%H A036511 Giovanni Resta, <a href="/A036511/b036511.txt">Table of n, a(n) for n = 1..20</a>
%t A036511 a[n_] := Block[{k=1}, While[DigitCount[k^2, 10, 4] != n, k++]; k^2]; Array[a, 7] (* _Giovanni Resta_, Jul 27 2018 *)
%Y A036511 Cf. A048349. - _Jon E. Schoenfield_, Jan 24 2009
%K A036511 nonn,base
%O A036511 1,1
%A A036511 _David W. Wilson_
%E A036511 a(13)-a(16) from _Jon E. Schoenfield_, Jan 17 2009
%E A036511 a(17) from _Giovanni Resta_, Jul 27 2018