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A079324
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k such that 2kp+1 is the first factor of a nonprime Mersenne number M(p) = 2^p - 1.
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2
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1, 1, 4, 3, 163, 5, 25, 60, 1525, 1445580, 1609, 3, 17, 1, 59, 36793758459, 12379533, 3421967, 15, 1, 116905896337578232, 20236572837, 290792847537859675, 60, 2713800, 461, 7033, 2112, 1, 120, 1, 35807, 19, 413328944, 36, 41
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OFFSET
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1,3
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COMMENTS
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a(188) = 216 = k = (f-1)/2p for p=1231, f=531793. Although Mersenne numbers with p = 1213, 1217, 1229, 1231 are not fully factored, we know their smallest factors. One factor is known for p=1237 but it is not certain that it is the smallest. - Gord Palameta, Sep 26 2018
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LINKS
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EXAMPLE
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2^11 - 1 = 23*89, 23 = 2*1*11 + 1, therefore a(1) = 1.
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PROG
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(PARI) forprime (n=3, 101, v=2^n-1; if (!isprime(v), print1((factor(v)[, 1][1]-1)\(2*n)", ")))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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