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%I #34 Jul 22 2021 23:29:37
%S 1,3,9,15,27,37,165,207,897,5761,16753,17995,96567
%N Numbers k such that (10^k*361 - 163)/9 is prime (k > 0).
%C a(14) > 10^5. - _Robert Price_, Oct 31 2017
%e If k = 1 then (10^1*361 - 163)/9 = 383 (prime), so 1 is a term.
%e If k = 9 then (10^9*361 - 163)/9 = 40111111093 (prime), so 9 is a term.
%t ParallelMap[ If[ PrimeQ[ (10^# 361-163)/9], #, Nothing] &, Range[6000]]
%Y Cf. A247643.
%K nonn,hard,more
%O 1,2
%A _Mikk Heidemaa_, May 23 2017
%E a(13) from _Robert Price_, Oct 31 2017
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