A257771 Numbers n such that n*k - 1 and n*k + 1 are not both prime for any k < n.

1, 2, 5, 8, 11, 13, 31, 37, 53, 61, 73, 79, 97, 122, 127

Offset: 1

Author

Juri-Stepan Gerasimov, May 07 2015

Keywords

• nonn
• fini

Comments

Numbers n such that A071558(n) > n.

Crossrefs

Cf. A071558, A220141.

Programs

PARI

is(n)=for(k=1,n-1,if(isprime(n*k-1)&&isprime(n*k+1), return(0))); 1 \\ Charles R Greathouse IV, May 08 2015

PARI

is(n)=my(s=6/gcd(n,6)); forstep(k=s,n-1,s, if(isprime(n*k-1)&&isprime(n*k+1), return(0))); 1 \\ Charles R Greathouse IV, May 08 2015