A240765 Numbers n such that (43^n - 1)/42 is prime.

5, 13, 6277, 26777, 27299, 40031, 44773, 194119

Offset: 1

Author

Robert Price, Apr 12 2014

Keywords

• hard
• more
• nonn

Comments

a(8) > 10^5. - Robert Price, Apr 12 2014

Links

• H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
• H. 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.

Programs

Maple

A240765:=n->`if`(isprime((43^n - 1)/42), n, NULL); seq(A240765(n), n=1..100000); # Wesley Ivan Hurt, Apr 12 2014

Mathematica

Select[Prime[Range[100000]], PrimeQ[(43^#-1)/42]&]

PARI

is(n)=ispseudoprime((43^n-1)/42) \\ Charles R Greathouse IV, Feb 20 2017

Extensions

a(8) from Paul Bourdelais, Aug 04 2020