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%I #13 Jul 30 2023 01:38:18
%S 2,31,103,617,10253,10691,35353,129587,556441
%N Numbers k such that (10^k - 7^k)/3 is prime.
%C All terms are prime.
%C The corresponding primes: 17, 3333280741539321718064461652419, ...
%H Jon Grantham and Andrew Granville, <a href="https://arxiv.org/abs/2307.07894">Fibonacci primes, primes of the form 2^n-k and beyond</a>, arXiv:2307.07894 [math.NT], 2023.
%t Select[Range[1, 10000], PrimeQ[(10^# - 7^#)/3] &]
%o (PARI) for(n=1, 10000, if(isprime((10^n - 7^n)/3), print1(n, ", ")))
%Y Cf. A004023, A128026, A062576.
%K nonn,more,hard
%O 1,1
%A _Tim Johannes Ohrtmann_, May 21 2016
%E a(7)-a(9) from _Jon Grantham_, Jul 29 2023
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