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A015919
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Positive integers k such that 2^k == 2 (mod k).
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32
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1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 341, 347, 349, 353, 359, 367
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OFFSET
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1,2
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COMMENTS
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Includes 341 which is first pseudoprime to base 2 and distinguishes sequence from A008578.
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LINKS
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FORMULA
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MATHEMATICA
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Prepend[ Select[ Range@370, PowerMod[2, #, #] == 2 &], {1, 2}] // Flatten (* Robert G. Wilson v, May 16 2018 *)
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PROG
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(Python)
def ok(n): return pow(2, n, n) == 2%n
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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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