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A257531
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If 2^(n-1) mod n = 1, then 1 else 0.
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3
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0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0
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OFFSET
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1
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COMMENTS
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This first differs from A010051 (1 if n is prime, else 0) at the second term. The next position differing from A010051 is at the 341st term, and further divergences appear for odd pseudoprimes to base 2 (A001567).
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LINKS
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EXAMPLE
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a(341) = 1 as 2^340 mod 341 is 1.
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MAPLE
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[0, seq(`if`(2 &^ (n-1) mod n = 1, 1, 0), n = 2..104)]; # Peter Luschny, Sep 19 2017
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MATHEMATICA
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f[n_] := If[PowerMod[2, n - 1, n] == 1, 1, 0]; Array[f, 105] (* Robert G. Wilson v, Apr 28 2015 *)
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PROG
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CROSSREFS
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Characteristic function for A176997 (without its initial 1).
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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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