

A127995


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


23




OFFSET

1,1


REFERENCES

H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927930.


LINKS

Table of n, a(n) for n=1..7.
H. Lifchitz, Mersenne and Fermat primes field


MATHEMATICA

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


PROG

(Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 05 2010]
(Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 08 2010]


CROSSREFS

Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127996, A127997, A127998, A127999, A128000, A098438, A128002, A128003, A128004, A128005.
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)=31013 & a(6)=48859 are probable primes discovered by Paul Bourdelais, Mar 05 2010
a(7)=61403 is a probable prime discovered by Paul Bourdelais, Mar 08 2010


STATUS

approved



