A239637 Numbers n such that (41^n - 1)/40 is prime.

3, 83, 269, 409, 1759, 11731

Offset: 1

Author

Robert Price, Mar 22 2014

Keywords

• hard
• more
• nonn

Comments

a(7) > 10^5. - Robert Price, Mar 22 2014

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[100000]], PrimeQ[(41^#-1)/40]&]

PARI

isok(n) = isprime((41^n-1)/40); \\ Michel Marcus, Mar 13 2016