A127997 Numbers n such that (22^n - 1)/21 is prime.

2, 5, 79, 101, 359, 857, 4463, 9029, 27823

Offset

1,1

Comments

9029 is a term found by Richard Fischer in 2004. - Alexander Adamchuk, Feb 11 2007

No other terms < 100000. - Robert Price, Feb 25 2012

Links

Table of n, a(n) for n=1..9.

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[(22^#-1)/21]&]

Prog

(PARI) isok(n) = isprime((22^n-1)/21); \\ Michel Marcus, Mar 13 2016

Crossrefs

Sequence in context: A102983 A038583 A082080 * A096266 A123978 A303482

Adjacent sequences: A127994 A127995 A127996 * A127998 A127999 A128000

Keyword

hard,more,nonn

Author

Alexander Adamchuk, Feb 11 2007

Extensions

More terms from Ryan Propper, Mar 29 2007

27823 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008

Status

approved