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 A131539 #23 Jul 20 2024 08:19:02
%S A131539 0,8,16,76,41,1162,973,6838,25265,81782,456686,279270,1727606,6030753,
%T A131539 23157026,106892455
%N A131539 Exponent of least power of 2 having exactly n consecutive 5's in its decimal representation.
%H A131539 Popular Computing (Calabasas, CA), <a href="/A094776/a094776.jpg">Two Tables</a>, Vol. 1, (No. 9, Dec 1973), page PC9-16.
%e A131539 a(3)=76 because 2^76 (i.e., 75557863725914323419136) is the smallest power of 2 to contain a run of 3 consecutive fives in its decimal form.
%t A131539 a = ""; Do[ a = StringJoin[a, "5"]; b = StringJoin[a, "5"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
%K A131539 more,nonn,base
%O A131539 0,2
%A A131539 _Shyam Sunder Gupta_, Aug 26 2007
%E A131539 2 more terms from _Sean A. Irvine_, Jul 19 2010
%E A131539 a(13)-a(14) from _Lars Blomberg_, Jan 24 2013
%E A131539 a(0)=0 prepended by and a(15) from _Paul Geneau de Lamarlière_, Jul 19 2024