A127999 Numbers n such that (26^n - 1)/25 is prime.

7, 43, 347, 12421, 12473, 26717

Offset: 1

Author

Alexander Adamchuk, Feb 11 2007

Keywords

• hard
• more
• nonn

Comments

The next term after 347 is bigger than 2250. - Stefan Steinerberger, May 05 2007

No other terms less than 100000. - Robert Price, Mar 18 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[(26^#-1)/25]&]

PARI

is(n)=ispseudoprime((26^n-1)/25) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

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