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A127995 Numbers n such that (20^n - 1)/19 is prime. 8
3, 11, 17, 1487, 31013, 48859, 61403, 472709 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..8.

P. Bourdelais, A Generalized Repunit Conjecture

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[(20^#-1)/19]&]

PROG

(Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 05 2010]

CROSSREFS

Sequence in context: A128346 A128031 A194128 * A119141 A225144 A228470

Adjacent sequences:  A127992 A127993 A127994 * A127996 A127997 A127998

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Feb 11 2007

EXTENSIONS

One more term from Ryan Propper, Mar 29 2007

a(5) & a(6) are probable primes found by Paul Bourdelais, Mar 05 2010

a(7) is a probable prime found by Paul Bourdelais, Mar 08 2010

a(8) is a probable prime found by Paul Bourdelais, Jan 15 2015

STATUS

approved

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Last modified December 3 08:48 EST 2016. Contains 278698 sequences.