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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 (list; graph; refs; listen; history; text; internal format)
 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 Antti Karttunen, Table of n, a(n) for n = 2..10000 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 A344120 A090173 Adjacent sequences:  A056048 A056049 A056050 * A056052 A056053 A056054 KEYWORD easy,sign AUTHOR Robert G. Wilson v, Jul 25 2000 STATUS approved

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Last modified September 16 08:14 EDT 2021. Contains 347469 sequences. (Running on oeis4.)