This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A374105 #29 Sep 13 2024 08:43:05
%S A374105 2,5,7,11,541,1583,2713,2963,13831,22349,22669,23833,57287
%N A374105 Numbers k such that (9^k + 3^k + 1)/13 is prime.
%C A374105 Conjecturally all terms are prime. There are no composite terms < 24000.
%C A374105 57287 will be the next term if there are no composite terms below. There are no other prime terms < 100000.
%C A374105 Terms > 2963 correspond to probable primes.
%e A374105 5 is a term because (9^5 + 3^5 + 1)/13 = 4561 is prime.
%o A374105 (PARI) isok(k)={k%3 && ispseudoprime((9^k + 3^k + 1)/13)}
%o A374105 { for(k=1, 2000, if(isok(k), print1(k, ", "))) }
%Y A374105 Cf. A028491, A359436.
%K A374105 nonn,more
%O A374105 1,1
%A A374105 _Aurelien Gibier_, Jun 29 2024
%E A374105 a(13) confirmed by _Michael S. Branicky_, Sep 13 2024