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A128000 Numbers n such that (28^n - 1)/27 is prime. 2
2, 5, 17, 457, 1423, 115877 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No other terms less than 100000. - Robert Price, May 01 2012

LINKS

Table of n, a(n) for n=1..6.

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

Sequence in context: A111635 A041455 A081465 * A281312 A182313 A124374

Adjacent sequences:  A127997 A127998 A127999 * A128001 A128002 A128003

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

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Last modified February 19 13:20 EST 2020. Contains 332044 sequences. (Running on oeis4.)