A307390 - OEIS

%I #22 Aug 14 2024 17:57:10

%S 5,11,13,17,23,29,41,43,47,53,59,61,67,71,73,83,89,101,103,107,109,

%T 113,127,131,137,149,151,163,167,173,179,181,191,193,197,223,227,233,

%U 239,241,251,257,263,269,277,281,283,293,311,313,317,347,349,353,359,373,383,389,397,401,409,419,421

%N Primes p such that 2*p-1 is not prime.

%C Primes not in A005382.

%H Robert Israel, <a href="/A307390/b307390.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A109274(n) + 1. - _Bhavik Mehta_, Aug 14 2024

%e a(3) = 13 is in the sequence because 13 is prime but 2*13-1 = 25 is not.

%p select(t -> isprime(t) and not isprime(2*t-1), [seq(i,i=3..1000,2)]);

%Y Cf. A005382, A053176, A109274.

%Y Includes A007528.

%K nonn

%O 1,1

%A _Robert Israel_, Apr 17 2019