

A127995


Numbers n such that (20^n  1)/19 is prime.


10




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), 927930.
H. Lifchitz, Mersenne and Fermat primes field
Index to primes in various ranges, form ((k+1)^n1)/k


MATHEMATICA

Select[Prime[Range[100]], PrimeQ[(20^#1)/19]&]


PROG

(Other) PFGW v3.3.1  Paul Bourdelais, Mar 05 2010
(PARI) is(n)=isprime((20^n1)/19) \\ Charles R Greathouse IV, Feb 17 2017


CROSSREFS

Sequence in context: A128346 A128031 A194128 * A316839 A119141 A303520
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



