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 A370663 #11 Jul 08 2025 18:36:11 %S A370663 1,2,4,8,10,28,1348,1424,12838 %N A370663 Numbers k such that (9^k + 9*k)/9 is prime. %C A370663 If it exists, a(10) > 50000. %t A370663 Select[Range[1,13000],PrimeQ[((9^#+9*#) / 9)]&] (* _Vincenzo Librandi_, Jul 04 2025 *) %o A370663 (PARI) is(n) = ispseudoprime(9^(n-1)+n) %o A370663 (Magma) [n: n in [1..130] |IsPrime ((9^n + 9*n) div 9)]; // _Vincenzo Librandi_, Jul 04 2025 %Y A370663 Cf. A221911, A226202. %K A370663 nonn,hard,more %O A370663 1,2 %A A370663 _Hugo Pfoertner_, Feb 27 2024