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 A057900 #18 Mar 01 2024 14:17:37
%S A057900 2,8,34,1532,18248
%N A057900 Numbers k such that 3^k + k is prime.
%C A057900 Note that if n > 2 and n+1 is prime then (by Fermat's theorem) n+1 divides 3^n+n.
%C A057900 If it exists, a(6) > 100000. - _Hugo Pfoertner_, Mar 01 2024
%t A057900 Do[ If[ PrimeQ[ 3^n + n ], Print[ n ] ], {n, 0, 3000} ]
%t A057900 v={2}; Do[If[EvenQ[n]&&Mod[n, 3]!=0&&!PrimeQ[n+1]&&PrimeQ[3^n+n], v=Append[v, n]; Print[v]], {n, 3, 19000}]
%t A057900 Select[Range[18500],PrimeQ[3^#+#]&] (* _Harvey P. Dale_, Jul 23 2013 *)
%o A057900 (PARI) is(n)=ispseudoprime(3^n+n) \\ _Charles R Greathouse IV_, May 22 2017
%Y A057900 Cf. A104743, A052007, A057909.
%K A057900 nonn,hard,more
%O A057900 1,1
%A A057900 _Robert G. Wilson v_, Nov 16 2000
%E A057900 18248 from _Farideh Firoozbakht_, Aug 21 2003