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Search: id:A005420
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| A005420 |
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Largest prime factor of 2^n - 1.
(Formerly M2609)
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+0
9
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| 3, 7, 5, 31, 7, 127, 17, 73, 31, 89, 13, 8191, 127, 151, 257, 131071, 73, 524287, 41, 337, 683, 178481, 241, 1801, 8191, 262657, 127, 2089, 331, 2147483647, 65537, 599479, 131071, 122921, 109, 616318177, 524287, 121369, 61681, 164511353, 5419
(list; graph; listen)
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OFFSET
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2,1
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
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LINKS
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T. D. Noe, Table of n, a(n) for n=2..500 (derived from Brillhart et al.)
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
S. S. Wagstaff, Jr., The Cunningham Project
Eric Weisstein's World of Mathematics, Mersenne Number
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EXAMPLE
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2^6-1 = 63 = 3*21 = 9*7, so a(6) = 7.
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PROGRAM
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(PARI) for(n=2, 44, v=factor(2^n-1); print1(v[matsize(v)[1], 1], ", "))
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CROSSREFS
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Sequence in context: A112927 A064078 A048857 this_sequence A161818 A161509 A108974
Adjacent sequences: A005417 A005418 A005419 this_sequence A005421 A005422 A005423
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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Description corrected by Michael Somos, Feb 24, 2002
More terms from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Aug 22 2002
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