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

1,1

References

E.I. Ignatjew, Mathematische Spielereien, Urania Verlag Leipzig-Jena-Berlin, 2. Auflage 1982

Links

Table of n, a(n) for n=1..47.

Example

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

Prog

(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<<k, s)==n, return(k)))

Crossrefs

Cf. A018802, A171132, A171242, A171489, A171617

Sequence in context: A207141 A256958 A165871 * A078289 A043618 A296874

Adjacent sequences: A171649 A171650 A171651 * A171653 A171654 A171655

Keyword

nonn,base

Author

Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Dec 14 2009

Extensions

More terms, program, and editing by Charles R Greathouse IV, Aug 02 2010

Status

approved