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A232931 The least positive integer k such that Kronecker(D/k) = -1 where D runs through all positive fundamental discriminants (A003658). 9
2, 3, 5, 2, 3, 2, 7, 5, 2, 5, 2, 7, 3, 3, 2, 3, 5, 13, 2, 3, 2, 5, 7, 2, 2, 5, 3, 3, 2, 5, 2, 3, 11, 2, 3, 11, 7, 7, 2, 7, 3, 3, 2, 7, 2, 3, 11, 2, 3, 2, 5, 5, 2, 5, 2, 11, 3, 3, 5, 2, 7, 11, 2, 3, 2, 5, 7, 2, 2, 5, 3, 3, 2, 7, 3, 11, 2, 3, 7, 7, 5, 2, 5, 2, 13, 3, 3, 2, 2, 3, 2, 3, 2, 5, 5, 11, 2, 7, 5, 3, 3, 5, 2, 3, 13, 5, 2, 3, 2, 17, 2, 2, 7, 3, 3, 2, 13, 2, 5, 2, 3, 5, 7, 5, 2, 5, 2, 11, 3, 2, 5, 2, 3, 7, 2, 3, 2, 17, 5, 7, 2, 7, 2, 5, 3, 3, 7, 2, 3, 7, 5, 2, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

From Jianing Song, Jan 30 2019: (Start)

a(n) is necessarily prime. Otherwise, if a(n) is not prime, we have (D/p) = 0 or 1 for all prime divisors p of a(n), so (D/a(n)) must be 0 or 1 too, a contradiction.

a(n) is the least inert prime in the real quadratic field with discriminant D, D = A003658(n). (End)

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 2..10000

S. R. Finch, Average least nonresidues, December 4, 2013. [Cached copy, with permission of the author]

Andrew Granville, R. A. Mollin and H. C. Williams, An upper bound on the least inert prime in a real quadratic field, Canad. J. Math. 52:2 (2000), pp. 369-380.

P. Pollack, The average least quadratic nonresidue modulo m and other variations on a theme of Erdős, J. Number Theory 132 (2012) 1185-1202.

Enrique Treviño, The least inert prime in a real quadratic field, Mathematics of Computation 81:279 (2012), pp. 1777-1797. See also his PANTS 2010 talk.

FORMULA

With D = A003658(n): Mollin conjectured, and Granville, Mollin, & Williams prove, that for n > 1128, a(n) <= D^0.5 / 2. Treviño proves that for n > 484, a(n) <= D^0.45. Asymptotically the exponent is less than 0.16. - Charles R Greathouse IV, Apr 23 2014

a(n) = A092419(A003658(n) - floor(sqrt(A003658(n))), n >= 2. - Jianing Song, Jan 30 2019

EXAMPLE

A003658(3) = 8, (8/3) = -1 and (8/2) = 0, so a(3) = 3.

MATHEMATICA

nMax = 200; A003658 = Select[Range[4nMax], NumberFieldDiscriminant[Sqrt[#]] == #&]; f[d_] := For[k = 1, True, k++, If[FreeQ[{0, 1}, KroneckerSymbol[d, k]], Return[k]]]; a[n_] := f[A003658[[n]]]; Table[a[n], {n, 2, nMax}] (* Jean-François Alcover, Nov 05 2016 *)

PROG

(PARI) lp(D)=forprime(p=2, , if(kronecker(D, p)<0, return(p)))

for(n=5, 1e3, if(isfundamental(n), print1(lp(n)", "))) \\ Charles R Greathouse IV, Apr 23 2014

CROSSREFS

Cf. A003658, A092419, A241482.

Sequence in context: A133906 A317358 A133907 * A060084 A265668 A273087

Adjacent sequences:  A232928 A232929 A232930 * A232932 A232933 A232934

KEYWORD

nonn

AUTHOR

Steven Finch, Dec 02 2013

EXTENSIONS

Name simplified by Jianing Song, Jan 30 2019

STATUS

approved

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Last modified September 16 12:57 EDT 2019. Contains 327113 sequences. (Running on oeis4.)