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A057187 Numbers n such that (21^n+1)/22 is a prime. 13
3, 5, 7, 13, 37, 347, 17597, 59183, 80761, 210599 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Some of the larger terms may only correspond to probable primes.

Searching to n=100000. [From Paul Bourdelais, Mar 24 2010]

LINKS

Table of n, a(n) for n=1..10.

H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.

H. Lifchitz, Mersenne and Fermat primes field

Paul Bourdelais,A Generalized Repunit Conjecture [From Paul Bourdelais, Mar 24 2010]

PROG

(Prime95) PRP=1, 21, 210599, 1, 0, 0, "22"

CROSSREFS

Sequence in context: A047933 A075557 A244452 * A163080 A141414 A236464

Adjacent sequences:  A057184 A057185 A057186 * A057188 A057189 A057190

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Sep 15 2000

EXTENSIONS

17597 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008

a(8)=59183 is a probable prime discovered by Paul Bourdelais, Mar 22 2010

a(9)=80761 is a probable prime discovered by Paul Bourdelais, Mar 24 2010

a(10)=210599 is a probable prime discovered by Paul Bourdelais, Aug 30 2013

STATUS

approved

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Last modified March 28 02:40 EDT 2017. Contains 284182 sequences.