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A015911
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Numbers k such that 2^k mod k is odd.
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12
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25, 45, 55, 91, 95, 99, 125, 135, 143, 153, 155, 161, 175, 187, 225, 235, 245, 247, 261, 273, 275, 279, 285, 289, 297, 319, 329, 333, 335, 355, 363, 369, 387, 391, 403, 407, 413, 423, 425, 429, 435, 437, 441, 459, 473, 477, 481, 483, 493, 507, 517, 525, 529
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OFFSET
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1,1
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COMMENTS
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All terms are composite: due to Fermat's little theorem, 2^p == 2 (mod p) when p is prime. - M. F. Hasler, May 10 2021
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LINKS
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MAPLE
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q:= n-> is(2&^n mod n, odd):
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MATHEMATICA
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Select[Range@532, OddQ@PowerMod[2, #, # ] &]
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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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STATUS
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approved
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