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%I #13 Oct 17 2023 11:16:17
%S 3,294277,735439
%N Numbers k such that (34^k + 1)/35 is prime.
%C These are the repunits in base -34.
%H Paul Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a>
%e 3 is a term since (34^3 + 1)/35 = 1123 is a prime.
%t Do[ If[ PrimeQ[ (34^n+1)/35], Print[n]], {n, 0, 18000}]
%o (PARI) is(n) = my(q=(34^n+1)/35); (denominator(q)==1) && ispseudoprime(q);
%Y Cf. A185230.
%K nonn,bref,hard,more
%O 1,1
%A _Paul Bourdelais_, Oct 16 2023