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Numbers k such that 10*k! + 1 is prime.
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%I #26 Jul 07 2024 22:32:44

%S 0,1,3,4,5,23,32,39,61,349,718,805,1025,1194,1550,1774,3417,7583

%N Numbers k such that 10*k! + 1 is prime.

%C a(17) > 2880. - _Jinyuan Wang_, Feb 05 2020

%C a(19) > 12000. - _Michael S. Branicky_, Jul 07 2024

%e k = 4 is a term because 10*4! + 1 = 241 is prime.

%o (PARI) is(k) = ispseudoprime(10*k!+1); \\ _Jinyuan Wang_, Feb 05 2020

%Y Cf. A002981, A051915, A076679, A076680, A076681, A076682, A076683, A178488, A180626.

%K nonn,more

%O 1,3

%A _Parthasarathy Nambi_, May 07 2007

%E a(15)-a(16) from _Jinyuan Wang_, Feb 05 2020

%E a(17) from _Michael S. Branicky_, Apr 16 2023

%E a(18) from _Michael S. Branicky_, Jul 07 2024