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Least exponent k such that the lowest n digits in the decimal representation of 2^k are even.
1

%I #13 Nov 13 2017 21:56:23

%S 1,6,10,11,19,43,50,50,71,71,523,590,590,12106,12106,12106,12106,

%T 56590,505206,1570511,1570511,4033966,4033966,9525771,24045606,

%U 24045606,57862019,183002599,183002599,877875719,877875719,877875719,3789535319

%N Least exponent k such that the lowest n digits in the decimal representation of 2^k are even.

%C This problem was discussed in a thread "Power of 2 with all even digits?" in the newsgroup sci.math (Jun 25 2004) with contributions from Edwin Clark, James Waldby, Bertram Felgenhauer, Richard Tobin, Oskar Lanzi III and others.

%H Newsgroup sci.math, <a href="http://mathforum.org/kb/message.jspa?messageID=581881">Power of 2 with all even digits?</a>

%e a(5)=19 because 2^19=524288 is the smallest power of 2 that has a decimal representation ending in 5 even digits.

%Y Cf. A000079, A068994.

%K base,nonn

%O 1,2

%A _Hugo Pfoertner_, Jul 07 2004

%E a(21) - a(35) from Richard Tobin (richard(AT)cogsci.ed.ac.uk), Jun 29 2004