

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
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OFFSET

1,2


COMMENTS

Numbers n such that A071558(n) > n.


LINKS

Table of n, a(n) for n=1..15.


PROG

(PARI) is(n)=for(k=1, n1, if(isprime(n*k1)&&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, n1, s, if(isprime(n*k1)&&isprime(n*k+1), return(0))); 1 \\ Charles R Greathouse IV, May 08 2015


CROSSREFS

Cf. A071558, A220141.
Sequence in context: A190057 A190305 A294391 * A276881 A282457 A329848
Adjacent sequences: A257768 A257769 A257770 * A257772 A257773 A257774


KEYWORD

nonn,fini


AUTHOR

JuriStepan Gerasimov, May 07 2015


STATUS

approved



