A128005 Numbers n such that (40^n - 1)/39 is prime.

2, 5, 7, 19, 23, 29, 541, 751, 1277

Offset: 1

Author

Alexander Adamchuk, Feb 11 2007

Keywords

• hard
• more
• nonn

Comments

No other terms for n < 100000. - Robert Price, Jan 27 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[(40^#-1)/39]&]

PARI

isok(n) = isprime((40^n-1)/39); \\ Michel Marcus, Mar 13 2016

Extensions

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