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Search: id:A046865
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| A046865 |
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Numbers n such that 4*5^n -1 is prime. |
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+0
10
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| 1, 3, 9, 13, 15, 25, 39, 69, 165, 171, 209, 339, 2033, 6583, 15393
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17.
R. K. Guy, Unsolved Problems in Number Theory, Section A3.
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LINKS
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Steven Harvey, Williams Primes
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MATHEMATICA
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Do[ If[ PrimeQ[4*5^n - 1], Print[n]], {n, 1, 8100, 2}]
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CROSSREFS
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Cf. A003307, A002235, A079906, A046866, A001771, A005541, A056725, A046867, A079907.
Sequence in context: A029458 A050571 A111230 this_sequence A063791 A077791 A163595
Adjacent sequences: A046862 A046863 A046864 this_sequence A046866 A046867 A046868
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KEYWORD
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nonn,hard,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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Two more terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 16 2003 and Jan 26 2003
15393 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
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