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A071558 Smallest k such that nk+1 and nk-1 are simultaneously primes. 2
4, 2, 2, 1, 6, 1, 6, 9, 2, 3, 18, 1, 24, 3, 2, 12, 6, 1, 12, 3, 2, 9, 6, 3, 6, 12, 4, 15, 12, 1, 42, 6, 6, 3, 12, 2, 54, 6, 8, 6, 30, 1, 24, 15, 4, 3, 6, 4, 18, 3, 2, 6, 120, 2, 12, 48, 4, 6, 18, 1, 258, 21, 14, 3, 30, 3, 24, 15, 2, 6, 18, 1, 84, 27, 2, 3, 6, 4, 132, 3, 10, 15, 54, 5, 12, 12 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

LINKS

T. D. Noe, Table of n, a(n) for n=1..1000

PROG

(PARI) for(n=1, 100, s=1; while(isprime(s*n+1)*isprime(n*s-1)==0, s++); print1(s, ", "))

CROSSREFS

Cf. A071256

Sequence in context: A205032 A088570 A102888 * A179621 A136709 A137239

Adjacent sequences:  A071555 A071556 A071557 * A071559 A071560 A071561

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre (benoit7848c(AT)orange.fr), May 30 2002

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Last modified February 16 18:43 EST 2012. Contains 205939 sequences.