A374155 - OEIS

%I #13 Jun 29 2024 11:22:00

%S 2,3,5,2,3,3,2,5,2,5,2,3,2,11,2,7,3,3,17,2,2,2,3,2,2,5,2,3,3,2,2,3,2,

%T 5,5,2,3,41,2,13,3,3,2,2,7,2,5,2,3,3,2,2,2,3,2,2,5,2,3,2,7,17,7,2,2,7,

%U 5,2,3,3,2,2,2,3,5,2,5,3,2,2,3,3,2,2,2

%N a(n) is the least prime that is a quadratic residue modulo prime(n). First column of A373751.

%e a(38) = 41 because row 38 of A373751 starts 41, 43, 47, ..., which are the primes that are quadratic residues modulo 163.

%p a := proc(n) local a, p; a := 1; p := ithprime(n); while true do a := a + 1;

%p if NumberTheory:-QuadraticResidue(a, p) = 1 and isprime(a) then return a fi od end: seq(a(n), n = 1..85);

%o (PARI) a(n) = my(p=prime(n), q=2); while (!issquare(Mod(q, p)), q=nextprime(q+1)); q; \\ _Michel Marcus_, Jun 29 2024

%Y Variant: A306530 (differs in the first 3 values).

%Y Cf. A373751.

%K nonn

%O 1,1

%A _Peter Luschny_, Jun 29 2024