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A124244 a(n) is the smallest odd prime p such that 2^n*p has n digits but has at most two distinct digits; or 0 if no such prime exists. 1
3, 3, 29, 101, 691, 15467, 39023, 71023, 437977, 4344227, 21158903, 109739989, 344590189, 2956838897, 6781690193, 0, 85533990571, 3390460543777, 0, 53936545044581, 0, 0, 5298071316879193, 0, 168548719780643483 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Andrew Rupinski showed that a(95) exists (see the links below).
LINKS
Prime Puzzles & Problems Connection, Puzzle 376. n=p*2^x.
Andrew Rupinski, Prime Curios!.
EXAMPLE
a(14)=2956838897 because 2^14*2956838897=48444848488448 has 14 digits with two distinct digits and 2956838897 is the smallest prime p such that 2^14*p has these properties.
MATHEMATICA
a[1]=3; a[n_]:=(For[m=Floor[5^(n-1)/2], !(PrimeQ[m]&&Length[Union[ IntegerDigits[2^n*m]]]==2&&Length[IntegerDigits[2^n*m]]==n), m++ ]; m); Do[Print[a[n]], {n, 14}]
CROSSREFS
Cf. A124245.
Sequence in context: A138962 A139206 A100651 * A351990 A151480 A096351
KEYWORD
nonn,base
AUTHOR
Farideh Firoozbakht, Oct 25 2006
EXTENSIONS
Edited by Don Reble, Oct 29 2006
STATUS
approved

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Last modified May 28 12:54 EDT 2024. Contains 372913 sequences. (Running on oeis4.)