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 A226163 Determinant of the (p_n-1)/2-by-(p_n-1)/2 matrix with (i,j)-entry being the Legendre symbol ((i^2-((p_n-1)/2)!*j)/p_n), where p_n is the n-th prime. 6
 0, -1, 0, 0, -8, -72, 0, 0, -2061248, 0, -18150912, 2581719040, 0, 0, 6237406973952, 0, 311692729699401728, 0, 0, 2675112340760315428864, 0, 0, -149670892669766097645487521792, 162894623351898578070944297779200, 273248864699809403831952842162176, 0, 0, -13518055482368485085619549462056665088, 4364947372586985974930810143672643878912 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,5 COMMENTS Conjecture: a(n) = 0 if and only if p_n == 3 (mod 4). Note that for an odd prime p we have (((p-1)/2)!)^2 == (-1)^{(p+1)/2} (mod p) by Wilson's theorem. In 1961, Mordell proved that((p-1)/2)! == (-1)^{(h(-p)+1)/2} (mod p) for any prime p > 3 with p == 3 (mod 4), where h(-p) is the class number of the imaginary quadratic field Q(sqrt(-p)). LINKS Zhi-Wei Sun, Table of n, a(n) for n = 2..80 L. J. Mordell, The congruence ((p-1)/2)! == 1 or -1 (mod p), Amer. Math. Monthly 68 (1961), 145-146. Zhi-Wei Sun, A conjecture on Legendre symbol determinants, a message to Number Theory List, July 17, 2013. EXAMPLE a(2) = 0 since the Legendre symbol ((1^2-1)/3) is equal to 0. MATHEMATICA a[n_]:=Det[Table[JacobiSymbol[i^2-((Prime[n]-1)/2)!*j, Prime[n]], {i, 1, (Prime[n]-1)/2}, {j, 1, (Prime[n]-1)/2}]] Table[a[n], {n, 2, 30}] CROSSREFS Cf. A227609, A227968, A227971. Sequence in context: A294166 A203008 A235128 * A004165 A032554 A097255 Adjacent sequences:  A226160 A226161 A226162 * A226164 A226165 A226166 KEYWORD sign AUTHOR Zhi-Wei Sun, Aug 05 2013 STATUS approved

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Last modified May 26 18:08 EDT 2020. Contains 334630 sequences. (Running on oeis4.)