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Search: id:A124244
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| A124244 |
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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. |
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+0
2
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| 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; listen)
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OFFSET
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1,1
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COMMENT
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Andrew Rupinski showed that a(95) exists (see the links below).
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LINKS
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Prime Puzzles & Problems Connection, Puzzle 376. n=p*2^x.
Andrew Rupinski, Prime Curios!.
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EXAMPLE
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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.
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MATHEMATICA
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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}]
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CROSSREFS
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Cf. A124245.
Adjacent sequences: A124241 A124242 A124243 this_sequence A124245 A124246 A124247
Sequence in context: A138962 A139206 A100651 this_sequence A096351 A086667 A067098
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KEYWORD
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nonn,base
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Oct 25 2006
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EXTENSIONS
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Edited by Don Reble (djr(AT)nk.ca), Oct 29 2006
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