A256823 Numbers n such that A257378(n)=A257379(n), so the prime numbers k*n*2^n-1 and k*n*2^n+1 are twin primes for the smallest k such that k*n*2^n-1 is a prime number.

4, 7, 9, 11, 27, 40, 63, 80, 120, 173, 227, 358, 445, 525, 767, 1164, 2180, 5368, 7898

Offset: 1

Author

Pierre CAMI, Apr 24 2015

Keywords

• nonn
• more

Comments

The k values are in A257378 and A257379.

Crossrefs

Cf. A257378, A257379.

Programs

PARI

a8(n) = my(k=1); while(!isprime(k*n*2^n+1), k+=2); k;
a9(n) = my(k=1); while(!isprime(k*n*2^n-1), k+=2); k;
isok(n) = a8(n) == a9(n); \\ Michel Marcus, Sep 15 2019