A171652 The initial decimal digits of 2^a(n) are the decimal digits of n followed by n.
50, 51, 25, 145, 142, 119, 86, 239, 93, 1558, 1598, 761, 1183, 6651, 5515, 4183, 34, 8990, 1343, 4180, 7987, 10628, 938, 5519, 4177, 10213, 10326, 6652, 1327, 5516, 12326, 4184, 11964, 6928, 6649, 8991, 653, 10373, 11549, 4181, 3706, 7988, 5862, 10629, 8988, 939, 13084
Offset: 1
Examples
a(1) = 50; 2^50 = 1125899906842624 a(2) = 51; 2^51 = 2251799813685248 a(3) = 25; 2^25 = 33554432 a(10) = 1558; 2^1558 = 10109583053...744
References
- E.I. Ignatjew, Mathematische Spielereien, Urania Verlag Leipzig-Jena-Berlin, 2. Auflage 1982
Programs
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PARI
double(n,k)=n\=10^(#Str(n)-2*k);if(n%10^k==n\=10^k,n) a(n)=my(s=#Str(n));for(k=1,1e6,if(double(1<
Extensions
More terms, program, and editing by Charles R Greathouse IV, Aug 02 2010