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Search: id:A091415
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| A091415 |
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Numbers n such that n!*2^n - 1 is prime. |
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+0
6
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| 2, 3, 4, 8, 13, 32, 41, 45, 59, 97, 107, 364, 421, 444, 1164, 1663, 3202, 4335, 4841, 13528, 22159
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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Ken Davis, Status of Search for Multifactorial Primes.
Ken Davis, Results for n!2-1.
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FORMULA
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a(n) = A007749[n+1]/2, where A007749[n] are the numbers n such that n!!-1 is prime. - Alexander Adamchuk (alex(AT)kolmogorov.com), Sep 23 2006
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EXAMPLE
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a(1)=2 because 2!*2^2 - 1 = 7 is prime
a(2)=3 because 3!*2^3 - 1 = 47 is prime
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MATHEMATICA
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For[n=1, n<1000, n++, If[PrimeQ[2^n*n!-1], Print[n]]] (Steinerberger)
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PROGRAM
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(PARI) f(n)=n!*2^n -1; for (i=1, 363, if(isprime(f(i)), print(i)))
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CROSSREFS
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A093173 gives the corresponding primes.
Cf. A007749, A117141, A092075.
Adjacent sequences: A091412 A091413 A091414 this_sequence A091416 A091417 A091418
Sequence in context: A126042 A076227 A092075 this_sequence A091816 A100993 A117395
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KEYWORD
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hard,nonn
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AUTHOR
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Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 02 2004
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EXTENSIONS
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a(12)-a(14) from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Feb 05 2006
a(15) from Mohammed Bouayoun (Mohammed.Bouayoun(AT)yahoo.fr), Apr 13 2006
More terms from Alexander Adamchuk (alex(AT)kolmogorov.com), Sep 23 2006
Corrected and extended by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008
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