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Search: id:A064998
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| A064998 |
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a(n) = smallest prime p such that p*n! +/- 1 are twin primes. |
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+0
1
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| 2, 2, 3, 2, 17, 7, 7, 3, 61, 29, 167, 401, 167, 19, 311, 461, 97, 919, 47, 71, 1483, 107, 13, 1571, 821, 1361, 769, 239, 163, 4229, 593, 373, 1571, 173, 6229, 3331, 1879, 2837, 2633, 12329, 2311, 269, 4159, 1217, 9719, 509, 3049, 8429, 307, 6121, 7919
(list; graph; listen)
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OFFSET
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2,1
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LINKS
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Harry J. Smith, Table of n, a(n) for n=2,...,200
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EXAMPLE
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a(6) = 17 because (17*6! = 12240) 12240 + 1 and 12240 -1 are twin primes and there is no prime less than 17 for which this pairing will work.
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MATHEMATICA
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Do[k = 1; While[ !PrimeQ[ Prime[k]*n! - 1] || !PrimeQ[ Prime[k]*n! + 1], k++ ]; Print[ Prime[k]], {n, 2, 75} ]
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PROGRAM
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(PARI) { allocatemem(932245000); for (n=2, 200, f=n!; p=2; while (!isprime(p*f + 1) || !isprime(p*f - 1), p=nextprime(p + 1)); write("b064998.txt", n, " ", p) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Oct 03 2009]
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CROSSREFS
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Cf. A051888, A064983.
Sequence in context: A016008 A016009 A110088 this_sequence A127012 A125503 A127009
Adjacent sequences: A064995 A064996 A064997 this_sequence A064999 A065000 A065001
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KEYWORD
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nonn
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AUTHOR
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Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 31 2001
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