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 A253774 #19 Nov 28 2023 16:01:47 %S A253774 1,3,15,81,327,357,685,831,861,1405,38571,78127,216487,546121,622615 %N A253774 Numbers k such that 4^k + 19 is prime. %F A253774 a(n) = A057221(n)/2. - _Joerg Arndt_, Aug 28 2015 %e A253774 15 is a term because 4^15 + 19 = 1073741843 is prime. %t A253774 Select[Range[3000], PrimeQ[4^# + 19] &] %o A253774 (Magma) [n: n in [0..700] | IsPrime(4^n+19)]; %o A253774 (PARI) is(n)=ispseudoprime(4^n+19) \\ _Charles R Greathouse IV_, Jun 06 2017 %Y A253774 Cf. A057221, A104068, A253772 (similar sequence). %K A253774 nonn,more %O A253774 1,2 %A A253774 _Vincenzo Librandi_, Jan 16 2015 %E A253774 Three more term (using A057221) from _Joerg Arndt_, Aug 28 2015 %E A253774 a(14)-a(15) derived from A057221 by _Elmo R. Oliveira_, Nov 28 2023