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 A131538 #23 Jul 20 2024 22:01:32
%S A131538 0,2,18,44,192,315,3396,8556,13327,81785,279267,865357,1799674,
%T A131538 1727603,8760851,63416791,106892452
%N A131538 Exponent of least power of 2 having exactly n consecutive 4's in its decimal representation.
%H A131538 Popular Computing (Calabasas, CA), <a href="/A094776/a094776.jpg">Two Tables</a>, Vol. 1, (No. 9, Dec 1973), page PC9-16.
%e A131538 a(3) = 44 because 2^44 (i.e. 17592186044416) is the smallest power of 2 to contain a run of 3 consecutive fours in its decimal form.
%t A131538 a = ""; Do[ a = StringJoin[a, "4"]; b = StringJoin[a, "4"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
%K A131538 more,nonn,base
%O A131538 0,2
%A A131538 _Shyam Sunder Gupta_, Aug 26 2007
%E A131538 3 more terms from _Sean A. Irvine_, Jul 19 2010
%E A131538 a(14) from _Lars Blomberg_, Jan 24 2013
%E A131538 a(15) from _Bert Dobbelaere_, Feb 25 2019
%E A131538 a(16) from _Paul Geneau de Lamarlière_, Jun 26 2024
%E A131538 a(0)=0 prepended by _Paul Geneau de Lamarlière_, Jul 20 2024