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A091997
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Numbers n such that 3*2^(n-1) - 1 is prime.
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2
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1, 2, 3, 4, 5, 7, 8, 12, 19, 35, 39, 44, 56, 65, 77, 95, 104, 144, 207, 217, 307, 325, 392, 459, 471, 828, 1275, 3277, 4205, 5135, 7560, 12677, 14899, 18124, 18820, 25691, 26460, 41629, 51388, 71784, 80331, 85688, 88172, 97064, 123631, 155931, 164988, 234761, 414841
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OFFSET
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1,2
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LINKS
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FORMULA
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EXAMPLE
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3*2^(3-1) - 1 = 11 so a(1) = 3.
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MATHEMATICA
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Do[If[PrimeQ[3*2^(n - 1) - 1], Print[n]], {n, 1, 8000}] (* Mohammed Bouayoun (Mohammed.Bouayoun(AT)yahoo.fr), Apr 13 2006 *)
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PROG
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(PARI) for (i=1, 1000, if(isprime(3*2^(i-1)-1), print1(i, ", ")))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 17 2004
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EXTENSIONS
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More terms from Mohammed Bouayoun (Mohammed.Bouayoun(AT)yahoo.fr), Apr 13 2006
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STATUS
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approved
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