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A059803 Numbers n such that 9^n - 8^n is prime or a strong pseudoprime. 13
2, 7, 29, 31, 67, 149, 401, 2531, 19913, 30773, 53857, 170099 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

In general, for any positive integers n, a and b, a>b, a necessary condition for a^n-b^n to be prime is that either a-b=1 and n be a prime or n=1 and a-b be prime (from Arturo Magidin and Hagman in Sci.Math, Sep 11, 2010). - Vincenzo Librandi, Sep 12 2010

LINKS

Table of n, a(n) for n=1..12.

PROG

(PARI) is(n)=ispseudoprime(9^n-8^n) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A000043, A057468, A059801, A059802, A062572-A062574, A062576-A062666.

Sequence in context: A191478 A321181 A122118 * A076043 A180448 A116968

Adjacent sequences:  A059800 A059801 A059802 * A059804 A059805 A059806

KEYWORD

nonn,hard

AUTHOR

Mike Oakes, Feb 23 2001

EXTENSIONS

Three more terms found by Jean-Louis Charton in 2004-2005: a(9) = 30773, a(10) = 53857, a(11) = 170099. - Alexander Adamchuk, Dec 08 2006

STATUS

approved

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Last modified October 17 08:36 EDT 2019. Contains 328107 sequences. (Running on oeis4.)