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

%I #14 May 30 2019 01:16:06

%S 5,8,12,18,20,22,25,28,30,31,33,37,39,41,42,44,46,47,49,53,54,58,60,

%T 61,63,67,69,74,84,86,88,92,93,94,96,100,102,104,105,106,109,110,114,

%U 117,119,120,125,128,133,138,143,145,146,153,155,156,158,160,165

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

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

%H Robert Israel, <a href="/A325438/b325438.txt">Table of n, a(n) for n = 1..10000</a>

%F A002496(a(n)) mod 10 = 1.

%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 = 1,i,NULL),i=1..nops(P));

%Y Cf. A002496, A325437, A325439.

%K nonn,base

%O 1,1

%A _Martin Renner_, Apr 27 2019