login
Indices of primes of the form k^2 + 1 ending in 7.
2

%I #13 May 30 2019 01:16:02

%S 3,4,6,7,9,10,11,13,14,15,16,17,19,21,23,24,26,27,29,32,34,35,36,38,

%T 40,43,45,48,50,51,52,55,56,57,59,62,64,65,66,68,70,71,72,73,75,76,77,

%U 78,79,80,81,82,83,85,87,89,90,91,95,97,98,99,101,103,107

%N Indices of primes of the form k^2 + 1 ending in 7.

%C This sequence is presumably infinite. See 1st comment of A002496.

%H Robert Israel, <a href="/A325439/b325439.txt">Table of n, a(n) for n = 1..10000</a>

%F A002496(a(n)) mod 10 = 7.

%p P:=[seq(k mod 10,k=select(isprime,[2,seq(4*i^2+1,i=1..10000)]))]:

%p seq(`if`(P[i] mod 10 = 7,i,NULL),i=1..nops(P));

%Y Cf. A002496, A325437, A325438.

%K nonn,base

%O 1,1

%A _Martin Renner_, Apr 27 2019