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A257771 Numbers n such that n*k - 1 and n*k + 1 are not both prime for any k < n. 0
1, 2, 5, 8, 11, 13, 31, 37, 53, 61, 73, 79, 97, 122, 127 (list; graph; refs; listen; history; text; internal format)
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, 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

Cf. A071558, A220141.

Sequence in context: A190057 A190305 A294391 * A276881 A282457 A329848

Adjacent sequences:  A257768 A257769 A257770 * A257772 A257773 A257774

KEYWORD

nonn,fini

AUTHOR

Juri-Stepan Gerasimov, May 07 2015

STATUS

approved

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Last modified February 26 01:41 EST 2020. Contains 332270 sequences. (Running on oeis4.)