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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

%I

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

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

%C Numbers n such that A071558(n) > n.

%o (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

%o (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

%Y Cf. A071558, A220141.

%K nonn,fini

%O 1,2

%A _Juri-Stepan Gerasimov_, May 07 2015

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Last modified February 5 03:48 EST 2023. Contains 360082 sequences. (Running on oeis4.)