A124245 a(n) is the smallest odd number m such that 2^n*m has n digits but has at most two distinct digits.

1, 3, 25, 101, 363, 3125, 15625, 71023, 390625, 1183713, 5474669, 27151397, 135646011, 1220703125, 6103515625, 18480090517, 85533990571, 762939453125, 3814697265625, 11550150977337, 53458791308981, 265147974756053

Offset

1,2

Comments

For each n, a(n) exists and is <= 5^(n-1).

Links

Table of n, a(n) for n=1..22.

The Prime Puzzles & Problems Connection, Puzzle 376. n=p*2^x.

Example

a(13)=135646011 because 2^13*135646011=1111212122112 has 13 digits with two distinct digits and 135646011 is the smallest odd number m such that 2^13*m has these properties.

Mathematica

a[1]=1; a[n_]:=(For[m=Floor[5^(n-1)/4], !(Length[Union[IntegerDigits [2^n*(2m-1)]]]==2&&Length[IntegerDigits[2^n*(2m-1)]]==n), m++ ]; 2m-1 ); Do[Print[a[n]], {n, 14}]

Crossrefs

Cf. A124244.

Sequence in context: A183761 A212054 A180324 * A360788 A166899 A201534

Adjacent sequences: A124242 A124243 A124244 * A124246 A124247 A124248

Keyword

nonn,base

Author

Farideh Firoozbakht, Oct 27 2006

Extensions

Edited by Don Reble, Oct 29 2006

Status

approved