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Numbers k such that 4*5^k + 1 is prime.
2

%I #27 Jan 04 2024 15:45:25

%S 0,2,6,18,50,290,2582,20462,23870,26342,31938,38122,65034,70130,

%T 245538,851878,1052422,1496566,5380542,8431178

%N Numbers k such that 4*5^k + 1 is prime.

%C All terms correspond to verified primes, that is, not merely probable primes. - _Robert Price_, Jan 16 2015

%C a(16) > 3*10^5. - _Robert Price_, Jan 16 2015

%t Select[Range[0,2000], PrimeQ[4*5^#+1]&]

%o (PARI) is(n)=ispseudoprime(4*5^n+1) \\ _Charles R Greathouse IV_, Jun 13 2017

%K nonn,more

%O 1,2

%A _José María Grau Ribas_, Jan 14 2012

%E a(8)-a(15) from _Robert Price_, Jan 16 2015

%E a(16)-a(19) from _Ryan Propper_, Dec 20 2023

%E a(20) from _Ryan Propper_, Jan 04 2024