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 A217383 #21 Apr 23 2025 18:52:23 %S A217383 3,7,11,47,81,95,107,179,233,243,947,2817,2859,3233,7563,11307,218615, %T A217383 225587,1160027 %N A217383 Numbers k such that 8^k - 9 is prime. %C A217383 All terms are equal to 1/3 of the multiples of 3 in A059610. %C A217383 Naturally these numbers are odd since 8^(2n)-9 = (8^n-3)(8^n+3) is composite. - _Bruno Berselli_, Oct 04 2012 %t A217383 Select[Range[10000], PrimeQ[8^# - 9] &] %o A217383 (PARI) is(n)=ispseudoprime(8^n-9) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A217383 Cf. A059610, A217356, A217382. %K A217383 nonn,more %O A217383 1,1 %A A217383 _Vincenzo Librandi_, Oct 03 2012 %E A217383 a(17)-a(18) using A059610 from _Michael S. Branicky_, Jul 14 2023 %E A217383 a(19) using A059610 from _Michael S. Branicky_, Apr 23 2025