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A038844
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n for which 6n+1 | 2^n-1.
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2
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5, 21, 37, 72, 73, 76, 100, 121, 153, 221, 233, 237, 245, 276, 288, 292, 296, 300, 305, 333, 336, 341, 348, 352, 357, 380, 381, 397, 445, 448, 461, 465, 472, 492, 545, 557, 565, 576, 577, 601, 605, 637, 648, 657, 676, 688, 692, 696, 737, 752, 753, 761, 776
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OFFSET
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1,1
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COMMENTS
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Apart from 5, all terms are in A045762, numbers such that 2^n-1 is not prime. - Michel Marcus, Nov 12 2014
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LINKS
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EXAMPLE
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For n=5, 2^5-1=31 is divisible by 6*5+1=31.
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MATHEMATICA
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Select[Range[800], PowerMod[2, #, 6#+1]==1&] (* Harvey P. Dale, Oct 24 2017 *)
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PROG
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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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