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A056051
a(n) = (n-2)! - 1 (mod n).
2
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
OFFSET
2,1
COMMENTS
(n-2)! - 1 is congruent to 0 iff n is a prime and is congruent to -1 iff n is a composite > 4.
LINKS
MATHEMATICA
Do[m = Mod[(n - 2)! - 1, n]; If[m < 2, Print[m], Print[m - n]], {n, 2, 100}]
PROG
(PARI) A056051(n) = { my(m=(((n-2)!-1)%n)); if(m < 2, m, m-n); }; \\ Antti Karttunen, Sep 14 2017, after Mathematica-code.
CROSSREFS
Cf. A005171.
Sequence in context: A178226 A288622 A095907 * A143541 A359583 A344120
KEYWORD
easy,sign
AUTHOR
Robert G. Wilson v, Jul 25 2000
STATUS
approved