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%I #16 Oct 28 2024 14:49:43
%S 0,1,2,5,7,9,11,14,22,45,54,67,74,321,706,902,962,11393,13605,17005,
%T 17364,27129,27674,29447
%N Numbers k such that 10*7^k + 1 is prime.
%C a(22) > 20169. - _Jinyuan Wang_, Jan 21 2020
%C a(25) > 50000. - _Michael S. Branicky_, Oct 28 2024
%t Do[ If[ PrimeQ[ 10*7^n + 1], Print[n]], {n, 1, 1000}]
%o (PARI) is(n)=ispseudoprime(10*7^n+1) \\ _Charles R Greathouse IV_, Jun 12 2017
%K nonn,more
%O 1,3
%A _Robert G. Wilson v_, Sep 08 2000
%E First term 0 inserted by and a(18)-a(21) from _Jinyuan Wang_, Jan 21 2020
%E a(22)-a(23) from _Michael S. Branicky_, Mar 20 2024
%E a(24) from _Michael S. Branicky_, Oct 28 2024