A215487 Numbers n such that (7^n - 2^n)/5 is prime.

3, 7, 19, 79, 431, 1373, 1801, 2897, 46997, 341063, 508867, 720497, 846913

Offset

1,1

Comments

All terms are prime.

a(14) > 10^6.

Links

Table of n, a(n) for n=1..13.

Jon Grantham and Andrew Granville, Fibonacci primes, primes of the form 2^n-k and beyond, arXiv:2307.07894 [math.NT], 2023.

Mathematica

Select[ Prime[ Range[1, 100000] ], PrimeQ[ ((7^# - 2^#)/5 ]& ]

Prog

(PARI) is(n)=ispseudoprime((7^n-2^n)/5) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Sequence in context: A217611 A322852 A243583 * A146037 A172514 A128024

Adjacent sequences: A215484 A215485 A215486 * A215488 A215489 A215490

Keyword

hard,more,nonn

Author

Robert Price, Aug 12 2012

Extensions

a(10)-a(13) from Jon Grantham, Jul 29 2023

Status

approved