OFFSET
1,1
COMMENTS
No other terms less than 100000. - Robert Price, May 01 2012
LINKS
H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
H. Lifchitz, Mersenne and Fermat primes field
Index to primes in various ranges, form ((k+1)^n-1)/k
MATHEMATICA
Select[Prime[Range[100]], PrimeQ[(28^#-1)/27]&]
PROG
(PARI) is(n)=ispseudoprime((28^n-1)/27) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 11 2007
EXTENSIONS
1423 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
a(6)=115877 corresponds to a probable prime discovered by Paul Bourdelais, Dec 08 2017
STATUS
approved