A273010 Numbers n such that (9^n - 7^n)/2 is prime.

3, 5, 7, 4703, 30113, 835391

Offset

1,1

Comments

All terms are prime.

The corresponding primes: 193, 21121, 1979713, ...

Links

Table of n, a(n) for n=1..6.

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

Mathematica

Select[Range[1, 10000], PrimeQ[(9^# - 7^#)/2] &]

Prog

(PARI) for(n=1, 10000, if(isprime((9^n - 7^n)/2), print1(n, ", ")))

Crossrefs

Cf. A081202, A173718, A128346, A059803.

Sequence in context: A191546 A069463 A288212 * A073691 A110336 A073695

Adjacent sequences: A273007 A273008 A273009 * A273011 A273012 A273013

Keyword

nonn,more,hard

Author

Tim Johannes Ohrtmann, May 13 2016

Extensions

a(6) from Jon Grantham, Jul 29 2023

Status

approved