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A005937
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Pseudoprimes to base 6.
(Formerly M5246)
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11
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35, 185, 217, 301, 481, 1105, 1111, 1261, 1333, 1729, 2465, 2701, 2821, 3421, 3565, 3589, 3913, 4123, 4495, 5713, 6533, 6601, 8029, 8365, 8911, 9331, 9881, 10585, 10621, 11041, 11137, 12209, 14315, 14701, 15841, 16589, 17329, 18361, 18721
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OFFSET
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1,1
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COMMENTS
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Theorem: If both numbers q and 2q-1 are primes and n=q*(2q-1) then 6^(n-1) == 1 (mod n) (n is in the sequence) iff q is of the form 12k+1. 2701, 18721, 49141, 104653, 226801, 665281, ... are such terms. This sequence is a subsequence of A122783. - Farideh Firoozbakht, Sep 12 2006
Composite numbers k such that 6^(k-1) == 1 (mod k). - Michel Lagneau, Feb 18 2012
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REFERENCES
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R. K. Guy, Unsolved Problems in Number Theory, A12.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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MATHEMATICA
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Select[Range[20000], ! PrimeQ[ # ] && PowerMod[6, #-1, # ] == 1 &] (* Farideh Firoozbakht, Sep 12 2006 *)
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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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