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Numbers k such that 2*5^k + 3 is prime.
1

%I #18 Oct 04 2022 19:10:02

%S 0,1,2,6,7,26,35,50,115,171,204,219,362,644,1959,4427,5406,8030,10755,

%T 67826

%N Numbers k such that 2*5^k + 3 is prime.

%C a(20) > 28465. - _Jinyuan Wang_, Dec 08 2019

%C a(21) > 10^5. - _Tyler NeSmith_, Oct 04 2022

%t Do[ If[ PrimeQ[ 2*5^n + 3 ], Print[ n ] ], {n, 0, 2000} ]

%o (PARI) is(n)=ispseudoprime(2*5^n+3) \\ _Charles R Greathouse IV_, Jun 13 2017

%K nonn,more

%O 1,3

%A _Robert G. Wilson v_, Nov 16 2000

%E First term 0 inserted by _Georg Fischer_, Aug 01 2019

%E a(17)-a(19) from _Jinyuan Wang_, Dec 08 2019

%E a(20) from _Tyler NeSmith_, Oct 04 2022