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%I #19 Jul 21 2024 12:48:20
%S 0,12,33,50,421,422,2187,15554,42483,42485,42486,1522085,2662514,
%T 6855863,6855865
%N Exponent of least power of 2 having exactly n consecutive 9's in its decimal representation.
%C Similarly to A006889, the least power of 2 to contain at least n consecutive 9's will always contain exactly n consecutive 9's. The previous power of two will contain exactly n-1 consecutive 9's preceded by a 4. - _Paul Geneau de Lamarlière_, Jul 20 2024
%C No more terms < 28*10^6.
%H Popular Computing (Calabasas, CA), <a href="/A094776/a094776.jpg">Two Tables</a>, Vol. 1, (No. 9, Dec 1973), page PC9-16.
%e a(3)=50 because 2^50 (i.e. 1125899906842624) is the smallest power of 2 to contain a run of 3 consecutive nines in its decimal form.
%t a = ""; Do[ a = StringJoin[a, "9"]; b = StringJoin[a, "9"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
%Y Cf. A006889.
%K more,nonn,base
%O 0,2
%A _Shyam Sunder Gupta_, Aug 26 2007
%E a(11) from _Sean A. Irvine_, May 31 2010
%E a(12)-a(14) from _Lars Blomberg_, Jan 24 2013
%E a(0)=0 prepended by _Paul Geneau de Lamarlière_, Jul 20 2024