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A059802
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Numbers k such that 5^k - 4^k is prime.
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111
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3, 43, 59, 191, 223, 349, 563, 709, 743, 1663, 5471, 17707, 19609, 35449, 36697, 45259, 91493, 246497, 265007, 289937
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OFFSET
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1,1
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COMMENTS
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Some of the larger terms may only correspond to probable primes.
5^1663 - 4^1663, a 1163-digit number, has been certified prime with Primo. - Rick L. Shepherd, Nov 13 2002
4 more terms found by Predrag Minovic in 2004: 35449, 36697, 45259, 91493. Corresponding numbers of decimal digits are 24778, 25651, 31635, 63951. - Alexander Adamchuk, Dec 02 2006
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LINKS
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Table of n, a(n) for n=1..20.
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MATHEMATICA
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Select[Range[1000], PrimeQ[5^# - 4^#] &] (* Alonso del Arte, Sep 09 2013 *)
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PROG
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(PARI) forprime(p=2, 1e5, if(ispseudoprime(5^p-4^p), print1(p", "))) \\ Charles R Greathouse IV, Jun 10 2011
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CROSSREFS
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Cf. A005060.
Cf. A000043, A057468, A059801, A128335, etc.
Sequence in context: A137192 A253577 A337213 * A139854 A194578 A185632
Adjacent sequences: A059799 A059800 A059801 * A059803 A059804 A059805
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KEYWORD
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nonn,hard
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AUTHOR
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Mike Oakes, Feb 23 2001
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EXTENSIONS
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New term 246497 found by Jean-Louis Charton in 2008 corresponding to a probable prime with 172295 digits - Jean-Louis Charton, Sep 02 2009
New term a(19) = 265007 found by Jean-Louis Charton, Feb 19 2013
a(20) = 289937 found by Jean-Louis Charton, Mar 15 2013
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STATUS
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approved
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