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A046865
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Numbers n such that 4*5^n -1 is prime.
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11
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1, 3, 9, 13, 15, 25, 39, 69, 165, 171, 209, 339, 2033, 6583, 15393
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| 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
| Steven Harvey, Williams Primes
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MATHEMATICA
| Do[ If[ PrimeQ[4*5^n - 1], Print[n]], {n, 1, 8100, 2}]
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CROSSREFS
| Cf. A003307, A002235, A079906, A046866, A001771, A005541, A056725, A046867, A079907.
Sequence in context: A050571 A193927 A111230 * A063791 A077791 A176393
Adjacent sequences: A046862 A046863 A046864 * A046866 A046867 A046868
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KEYWORD
| nonn,hard,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| 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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