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A071382
Numbers n such that (30^n+1)/31 is a prime.
15
139, 173, 547, 829, 2087, 2719, 3109, 10159, 56543, 80599
OFFSET
1,1
COMMENTS
Some of the larger terms may only correspond to probable primes.
a(11) > 10^5. - Robert Price, Jul 10 2013
LINKS
H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.
MATHEMATICA
Select[Range[3000], PrimeQ[(30^# + 1) / 31] &] (* Vincenzo Librandi, Oct 29 2017 *)
PROG
(PARI) isok(n) = (denominator(p=(30^n+1)/31)==1) && isprime(p); \\ Michel Marcus, Oct 29 2017
CROSSREFS
Cf. A071381.
Sequence in context: A325075 A020357 A050967 * A290450 A209618 A031928
KEYWORD
nonn,more
AUTHOR
Rick L. Shepherd, May 22 2002
EXTENSIONS
a(8) from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
a(9)-a(10) from Robert Price, Jul 10 2013
STATUS
approved