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 A275575 #31 Jan 16 2023 21:40:55 %S A275575 2,3,4,5,7,13,16,23,32,43,64,281,359,487,577,1579,1663,1741,3191,9209, %T A275575 11257,12743,13093,17027,26633,104243,134227,152287,700897,1205459 %N A275575 Numbers k such that (3^k + 1)/(3 - (-1)^k) is a prime. %p A275575 A275575:=n->`if`(isprime((3^n + 1)/(3 - (-1)^n)), n, NULL): seq(A275575(n), n=1..2*10^3); # _Wesley Ivan Hurt_, Dec 26 2016 %t A275575 Select[Range[0, 10^3], PrimeQ[(3^# + 1)/(3 - (-1)^#)] &] %o A275575 (PARI) isok(n) = isprime( (3^n + 1)/(3 - (-1)^n)); \\ _Michel Marcus_, Dec 26 2016 %Y A275575 Cf. A007658, A171381, A280083. %K A275575 nonn,more %O A275575 1,1 %A A275575 _Thomas Ordowski_, Dec 25 2016