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A056051
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a(n) = (n-2)! - 1 (mod n).
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2
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0, 0, 1, 0, -1, 0, -1, -1, -1, 0, -1, 0, -1, -1, -1, 0, -1, 0, -1, -1, -1, 0, -1, -1, -1, -1, -1, 0, -1, 0, -1, -1, -1, -1, -1, 0, -1, -1, -1, 0, -1, 0, -1, -1, -1, 0, -1, -1, -1, -1, -1, 0, -1, -1, -1, -1, -1, 0, -1, 0, -1, -1, -1, -1, -1, 0, -1, -1, -1, 0, -1, 0, -1, -1, -1, -1, -1, 0, -1, -1, -1, 0, -1, -1, -1, -1, -1, 0, -1, -1, -1, -1
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OFFSET
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2,1
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COMMENTS
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(n-2)! - 1 is congruent to 0 iff n is a prime and is congruent to -1 iff n is a composite > 4.
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LINKS
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MATHEMATICA
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Do[m = Mod[(n - 2)! - 1, n]; If[m < 2, Print[m], Print[m - n]], {n, 2, 100}]
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PROG
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(PARI) A056051(n) = { my(m=(((n-2)!-1)%n)); if(m < 2, m, m-n); }; \\ Antti Karttunen, Sep 14 2017, after Mathematica-code.
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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STATUS
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approved
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