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A171652 The initial decimal digits of 2^a(n) are the decimal digits of n followed by n.

%I A171652 #3 Mar 30 2012 17:28:26
%S A171652 50,51,25,145,142,119,86,239,93,1558,1598,761,1183,6651,5515,4183,34,
%T A171652 8990,1343,4180,7987,10628,938,5519,4177,10213,10326,6652,1327,5516,
%U A171652 12326,4184,11964,6928,6649,8991,653,10373,11549,4181,3706,7988,5862,10629,8988,939,13084
%N A171652 The initial decimal digits of 2^a(n) are the decimal digits of n followed by n.
%D A171652 E.I. Ignatjew, Mathematische Spielereien, Urania Verlag Leipzig-Jena-Berlin, 2. Auflage 1982
%e A171652 a(1) = 50; 2^50 = 1125899906842624
%e A171652 a(2) = 51; 2^51 = 2251799813685248
%e A171652 a(3) = 25; 2^25 = 33554432
%e A171652 a(10) = 1558; 2^1558 = 10109583053...744
%o A171652 (PARI) double(n,k)=n\=10^(#Str(n)-2*k);if(n%10^k==n\=10^k,n)
%o A171652 a(n)=my(s=#Str(n));for(k=1,1e6,if(double(1<<k,s)==n,return(k)))
%Y A171652 Cf. A018802, A171132, A171242, A171489, A171617
%K A171652 nonn,base
%O A171652 1,1
%A A171652 Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Dec 14 2009
%E A171652 More terms, program, and editing by _Charles R Greathouse IV_, Aug 02 2010