A245442 Numbers n such that (50^n - 1)/49 is prime.

3, 5, 127, 139, 347, 661, 2203, 6521, 210319

Offset: 1

Author

Robert Price, Jul 22 2014

Keywords

• hard
• more
• nonn

Comments

a(9) > 10^5.

All terms are prime.

Links

• Harvey Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
• Henri Lifchitz, Mersenne and Fermat primes field

Crossrefs

Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127995, A127996, A127997, A127998, A127999, A098438, A128002, A128003, A128004, A128005, A240765, A242797, A243279, A245237.

Programs

Maple

A245442:=n->`if`(isprime((50^n - 1)/49), n, NULL); seq(A245442(n), n=1..100000); # Wesley Ivan Hurt, Apr 12 2014

Mathematica

Select[Prime[Range[100000]], PrimeQ[(50^# - 1)/49] &]

PARI

is(n)=ispseudoprime((50^n-1)/49) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(9)=210319 corresponds to a probable prime discovered by Paul Bourdelais, Aug 04 2020