A307390 Primes p such that 2*p-1 is not prime.

5, 11, 13, 17, 23, 29, 41, 43, 47, 53, 59, 61, 67, 71, 73, 83, 89, 101, 103, 107, 109, 113, 127, 131, 137, 149, 151, 163, 167, 173, 179, 181, 191, 193, 197, 223, 227, 233, 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

Offset

1,1

Comments

Primes not in A005382.

Links

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

Formula

a(n) = A109274(n) + 1. - Bhavik Mehta, Aug 14 2024

Example

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

Maple

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

Crossrefs

Cf. A005382, A053176, A109274.

Includes A007528.

Sequence in context: A346416 A371449 A272446 * A104110 A038936 A106091

Adjacent sequences: A307387 A307388 A307389 * A307391 A307392 A307393

Keyword

nonn

Author

Robert Israel, Apr 17 2019

Status

approved