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 A303737 #9 Jun 07 2018 04:26:41 %S A303737 1,4,18,49,60,82,321,6328 %N A303737 Numbers k such that (2*k)! + k! - 1 is prime. %C A303737 a(9) > 10000. - _Giovanni Resta_, Jun 07 2018 %e A303737 1 is a term because (2*1)! + 1! - 1 = 2 which is a prime. %e A303737 4 is a term because (2*4)! + 4! - 1 = 40343 which is a prime. %p A303737 select(k->isprime(factorial(2*k)+factorial(k)-1),[$1..1000]); %o A303737 (PARI) isok(k) = isprime((2*k)! + k! - 1); \\ _Michel Marcus_, May 28 2018 %Y A303737 Cf. A242487, A300947, A303738 (corresponding primes). %K A303737 nonn,more %O A303737 1,2 %A A303737 _Muniru A Asiru_, May 27 2018 %E A303737 a(8) from _Giovanni Resta_, Jun 07 2018