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 A138699 #21 Apr 20 2019 11:10:29 %S A138699 2,3,13,21,231,849,885,1225,2955,10171 %N A138699 Numbers k such that 4^k - 3^k - 2^k is prime. %C A138699 a(10) > 7500. - _Derek Orr_, Apr 08 2014 %C A138699 a(11) > 10^5. - _Robert Price_, Apr 20 2019 %e A138699 4^2 - 3^2 - 2^2 = 16 - 9 - 4 = 3. %p A138699 A138699:=n->`if`(isprime(4^n - 3^n - 2^n), n, NULL); seq(A138699(n), n=1..1000); # _Wesley Ivan Hurt_, Apr 08 2014 %t A138699 Select[Range[11^3],PrimeQ[4^# - 3^# - 2^# ]&] %o A138699 (PARI) for(n=1, 7500, if(ispseudoprime(4^n - 3^n - 2^n), print1(n, ", "))) \\ _Derek Orr_, Apr 08 2014 %K A138699 nonn,more,hard %O A138699 1,1 %A A138699 _Vladimir Joseph Stephan Orlovsky_, May 15 2008 %E A138699 a(9) from _Derek Orr_, Apr 08 2014 %E A138699 a(10) from _Robert Price_, Apr 20 2019