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A231604
Numbers n such that (42^n + 1)/43 is prime.
5
3, 709, 1637, 17911, 127609, 172663
OFFSET
1,1
COMMENTS
The first 5 terms are primes.
LINKS
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.
Eric Weisstein's World of Mathematics, Repunit.
MATHEMATICA
Do[ p=Prime[n]; If[ PrimeQ[ (42^p + 1)/43 ], Print[p] ], {n, 1, 9592} ]
PROG
(PARI) is(n)=ispseudoprime((42^n+1)/43) \\ Charles R Greathouse IV, Feb 20 2017
KEYWORD
hard,more,nonn
AUTHOR
Robert Price, Nov 11 2013
EXTENSIONS
a(5)=127609 corresponds to a probable prime discovered by Paul Bourdelais, Jul 02 2018
a(6)=172663 corresponds to a probable prime discovered by Paul Bourdelais, Jul 29 2019
STATUS
approved