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A257771
Numbers n such that n*k - 1 and n*k + 1 are not both prime for any k < n.
1
1, 2, 5, 8, 11, 13, 31, 37, 53, 61, 73, 79, 97, 122, 127
OFFSET
1,2
COMMENTS
Numbers n such that A071558(n) > n.
PROG
(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
CROSSREFS
Sequence in context: A190057 A190305 A294391 * A276881 A282457 A329848
KEYWORD
nonn,fini
AUTHOR
STATUS
approved