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 A177863 Product modulo p of the quadratic nonresidues of p, where p = prime(n). 2
 1, 2, 1, 6, 10, 1, 1, 18, 22, 1, 30, 1, 1, 42, 46, 1, 58, 1, 66, 70, 1, 78, 82, 1, 1, 1, 102, 106, 1, 1, 126, 130, 1, 138, 1, 150, 1, 162, 166, 1, 178, 1, 190, 1, 1, 198, 210, 222, 226, 1, 1, 238, 1, 250, 1, 262, 1, 270, 1, 1, 282, 1, 306, 310, 1, 1, 330, 1, 346, 1, 1, 358, 366, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) == (-1)^((p-1)/2) (mod p), if p = prime(n) is odd. a(n)*A163366(n) == -1 (mod prime(n)), by Wilson's theorem. REFERENCES Carl-Erik Froeberg, On sums and products of quadratic residues, BIT, Nord. Tidskr. Inf.-behandl. 11 (1971) 389-398. LINKS Rahul Gupta, Algorithmic Number Theory, Section 24.5 FORMULA a(n) = A177861(n) modulo prime(n). EXAMPLE a(1) = 1 = the empty product, because there are no quadratic nonresidues of prime(1) = 2. a(4) = 6 because the quadratic nonresidues of prime(4) = 7 are 3, 5, and 6, and 3*5*6 = 90 == 6 (mod 7). MATHEMATICA Table[Mod[ Apply[Times, Flatten[Position[ Table[JacobiSymbol[i, Prime[n]], {i, 1, Prime[n] - 1}], -1]]], Prime[n]], {n, 1, 80}] CROSSREFS Cf. A177861 Product of the quadratic nonresidues of prime(n), A163366 Product modulo p of the quadratic residues of p, where p = prime(n). Sequence in context: A276664 A160565 A025252 * A193601 A157402 A069114 Adjacent sequences:  A177860 A177861 A177862 * A177864 A177865 A177866 KEYWORD easy,nonn AUTHOR Jonathan Sondow, May 14 2010 STATUS approved

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Last modified December 6 14:15 EST 2019. Contains 329806 sequences. (Running on oeis4.)