A265485 Numbers k such that 49^k - 7^k - 1 is prime.

1, 2, 12, 14, 110, 2574, 10964, 24257, 44364

Offset: 1

Author

Vincenzo Librandi, Dec 12 2015

Keywords

• nonn
• more

Comments

For k = 1, 2, 12, 14 the corresponding primes are 41, 2351, 191581231366725127199, 459986536544061737903951.

a(10) > 10^5. - Robert Price, Dec 25 2019

Examples

			2 is in the sequence because 49^2 - 7^2 - 1 = 2351 is prime.
		

Crossrefs

Cf. similar sequences listed in A265481.

Programs

Magma

[n: n in [0..1000] | IsPrime(49^n - 7^n - 1)];

Mathematica

Select[Range[2000], PrimeQ[49^# - 7^# - 1] &]

PARI

for(n=1, 1e3, if(ispseudoprime(49^n - 7^n - 1), print1(n, ", "))) \\ Altug Alkan, Dec 12 2015

Extensions

a(6) from Ray Chandler, Sep 25 2019

a(7)-a(9) from Robert Price, Dec 25 2019