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A098472
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Least k such that Mersenne-prime(n)*2^k-1 is prime (A000668(n)*2^k-1), or 0 if no such k exists.
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1
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1, 1, 1, 25, 1, 5, 1, 97, 77, 19, 37
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OFFSET
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1,4
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COMMENTS
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Conjecture: Mersenne-prime(12) is a Riesel prime (that is, all numbers k^2*M(12)-1 are composite for all k) and similarly for M(14) and M(15).
The sequence continues (>10000), 167, (>5000), (>5000), 1081, 371, 995, 909, 857, 33, (>150), (>150), ...
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LINKS
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MATHEMATICA
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mexp = {the list in A000043}; f[n_] := Block[{k = 1, mp = 2^mexp[[n]] - 1}, While[ !PrimeQ[ mp*2^k - 1] && k < 5000, k++ ]; If[k == 5000, 0, k]]; Do[ Print[ f[n]], {n, 20}] (* Robert G. Wilson v, Sep 11 2004 *)
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CROSSREFS
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KEYWORD
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hard,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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