login
A126856
Numbers n such that (31^n + 1)/32 is prime.
13
109, 461, 1061, 50777
OFFSET
1,1
COMMENTS
All terms are primes.
a(5) > 10^5. - Robert Price, Jul 12 2013
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[ (31^p + 1)/32 ], Print[p] ], {n, 1, 1100} ]
PROG
(PARI) is(n)=isprime((31^n+1)/32) \\ Charles R Greathouse IV, Feb 17 2017
KEYWORD
bref,hard,more,nonn
AUTHOR
Alexander Adamchuk, Mar 23 2007
EXTENSIONS
a(4) from Robert Price, Jul 12 2013
STATUS
approved