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Numbers whose least quadratic nonresidue (A020649) is 11.
10

%I #14 Oct 31 2020 04:35:52

%S 311,622,719,839,1009,1129,1201,1438,1511,1678,1801,2018,2258,2399,

%T 2402,2521,3022,3049,3191,3359,3361,3602,3889,4079,4201,4561,4679,

%U 4729,4798,4871,5039,5042,5209,5351,5591,5879,5881,6098,6359,6382,6718,6719,6722

%N Numbers whose least quadratic nonresidue (A020649) is 11.

%H Amiram Eldar, <a href="/A025024/b025024.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/QuadraticNonresidue.html">Quadratic Nonresidue</a>.

%t Select[Range[7000], Min @ Complement[Range[# - 1], Mod[Range[#/2]^2, #]] == 11 &] (* _Amiram Eldar_, Oct 31 2020 *)

%o (PARI) residue(n,m)=local(r);r=0;for(i=1,floor(m/2),if(i^2%m==n,r=1));r

%o isA025024(n)=local(a);a=1;forprime(p=2,7,a=a && residue(p,n));a=a && !residue(11,n);a \\ _Michael B. Porter_, Apr 30 2010

%o (PARI) is(n)=issquare(Mod(2,n)) && issquare(Mod(3,n)) && issquare(Mod(5,n)) && issquare(Mod(7,n)) && !issquare(Mod(11,n)) \\ _Charles R Greathouse IV_, Jan 24 2020

%Y Cf. A020649, A025020, A025021, A025022, A025023, A025025, A025026, A025027, A025028, A025029.

%K nonn

%O 1,1

%A _David W. Wilson_