A296922 Primes p such that Legendre(-5,p) = 0 or 1.

3, 5, 7, 23, 29, 41, 43, 47, 61, 67, 83, 89, 101, 103, 107, 109, 127, 149, 163, 167, 181, 223, 227, 229, 241, 263, 269, 281, 283, 307, 347, 349, 367, 383, 389, 401, 409, 421, 443, 449, 461, 463, 467, 487, 503, 509, 521, 523, 541, 547, 563, 569, 587, 601, 607, 641, 643

Offset: 1

Author

N. J. A. Sloane, Dec 25 2017

Keywords

• nonn

Comments

Primes == 1, 3, 5, 7, or 9 (mod 20). Primes whose 10's digit is even. - Robert Israel, Dec 27 2017

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A139513, A240920, A296920, A296923.

Programs

Maple

Load the Maple program HH given in A296920. Then run HH(-5,200);
select(isprime, {seq(seq(20*i+j,j=[1,3,5,7,9]),i=0..100)}); # Robert Israel, Dec 27 2017

Mathematica

Select[Prime@ Range@ 120, MemberQ[{0, 1}, KroneckerSymbol[-5, #]] &] (* or *)
Select[Prime@ Range@ 120, MemberQ[Range[1, 9, 2], Mod[#, 20]] &] (* Michael De Vlieger, Jan 02 2018 *)

PARI

lista(nn) = forprime(p=2, nn, if (kronecker(-5,p) >= 0, print1(p, ", "))); \\ Michel Marcus, Dec 26 2017

Formula

a(n) = A240920(n+1) for n >= 1. - Georg Fischer, Oct 30 2018