A025020 Numbers whose least quadratic nonresidue (A020649) is 2.

3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 15, 16, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 32, 33, 35, 36, 37, 38, 39, 40, 42, 43, 44, 45, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 63, 64, 65, 66, 67, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 83, 84, 85, 86, 87, 88, 90, 91, 92

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Quadratic Nonresidue.

Crossrefs

Cf. A020649, A025021, A025022, A025023, A025024, A025025, A025026, A025027, A025028, A025029.

Programs

Mathematica

Select[Range[100], Min @ Complement[Range[# - 1], Mod[Range[#/2]^2, #]] == 2 &] (* Amiram Eldar, Oct 31 2020 *)

PARI

isA025020(n)={local(r);r=1;for(m=1,n-1,if(m^2%n==2,r=0));r} \\ Michael B. Porter, Apr 16 2010