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 A071380 #21 Oct 02 2023 11:24:07 %S A071380 11,109,227,277,347,857,2297,9043,501409 %N A071380 Numbers n such that (26^n+1)/27 is a prime. %C A071380 Some of the larger terms may only correspond to probable primes. %C A071380 a(9) > 10^5. - _Robert Price_, Jul 07 2013 %H A071380 H. Dubner and T. Granlund, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/DUBNER/dubner.html">Primes of the Form (b^n+1)/(b+1)</a>, J. Integer Sequences, 3 (2000), #P00.2.7. %t A071380 Select[Range[3000], PrimeQ[(26^# + 1) / 27] &] (* _Vincenzo Librandi_, Oct 29 2017 *) %o A071380 (PARI) isok(n) = (denominator(p=(26^n+1)/27)==1) && isprime(p); \\ _Michel Marcus_, Oct 29 2017 %Y A071380 Cf. A057191, A071381. %K A071380 nonn,hard,more %O A071380 1,1 %A A071380 _Rick L. Shepherd_, May 22 2002 %E A071380 a(9) from _Paul Bourdelais_, Oct 02 2023