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

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

Offset: 1

Author

Alexander Adamchuk, Feb 11 2007

Keywords

• hard
• more
• nonn

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

• 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

Programs

Mathematica

Select[Prime[Range[100]],PrimeQ[(22^#-1)/21]&]

PARI

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

Extensions

More terms from Ryan Propper, Mar 29 2007

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