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

7, 43, 347, 12421, 12473, 26717

Offset

1,1

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

Table of n, a(n) for n=1..6.

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[(26^#-1)/25]&]

Prog

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

Crossrefs

Sequence in context: A042213 A193705 A164775 * A208595 A121675 A243273

Adjacent sequences: A127996 A127997 A127998 * A128000 A128001 A128002

Keyword

hard,more,nonn

Author

Alexander Adamchuk, Feb 11 2007

Extensions

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

Status

approved