A267943 Numbers n such that 2^n - 3 and 3*2^n - 1 are both prime.

3, 4, 6, 94

Offset: 1

Author

Arkadiusz Wesolowski, Jan 22 2016

Keywords

• nonn
• hard
• more

Comments

The intersection of A002235 and A050414 is not empty (3 does not belong to A267985).

Examples

			a(3) = 6 because 2^6 - 3 = 61 and 3*2^6 - 1 = 191 are both prime.
		

Crossrefs

Cf. A002235, A007505, A050414, A050415, A238694, A267985.

Programs

Magma

[n: n in [2..94] | IsPrime(2^n-3) and IsPrime(3*2^n-1)];

PARI

isok(n) = isprime(2^n-3) && isprime(3*2^n-1);

Formula

A002235 INTERSECT A050414.