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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
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
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 A373682 A166899
KEYWORD
nonn,base
AUTHOR
Farideh Firoozbakht, Oct 27 2006
EXTENSIONS
Edited by Don Reble, Oct 29 2006
STATUS
approved