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

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

Offset

1,1

Comments

No other terms for n < 100000. - Robert Price, Jan 27 2012

Links

Table of n, a(n) for n=1..9.

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[(40^#-1)/39]&]

Prog

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

Crossrefs

Sequence in context: A097052 A102937 A045358 * A045359 A042809 A002531

Adjacent sequences: A128002 A128003 A128004 * A128006 A128007 A128008

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