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 A296443 #30 Aug 08 2024 09:50:24 %S A296443 1,2,6,7,8,315,667,5125,7301,10500,11096 %N A296443 Numbers k such that 2*10^(2k)-2*10^k+1 is prime. %C A296443 Numbers of this form divide 4*10^(4k)+1. %C A296443 a(8) > 5000. - _Jon E. Schoenfield_, Dec 16 2017 %C A296443 a(12) > 25000. - _Michael S. Branicky_, Aug 08 2024 %e A296443 181, 19801, 1999998000001, 199999980000001, and 19999999800000001 are prime, while 1998001=277*7213, 199980001=13*41*457*821, and 19999800001=53*5953*63389. %t A296443 ParallelMap[If[PrimeQ[2*10^(2 #) - 2*10^# + 1], #, Nothing] &, Range@ 4000] (* _Robert G. Wilson v_, Dec 13 2017 *) %o A296443 (PARI) isok(k) = isprime(2*10^(2*k)-2*10^k+1); \\ _Michel Marcus_, Dec 13 2017 %Y A296443 See A296444 for 2*10^(2k)+2*10^k+1. %K A296443 nonn,more %O A296443 1,2 %A A296443 _Patrick A. Thomas_, Dec 13 2017 %E A296443 a(6)-a(7) from _Michel Marcus_, Dec 13 2017 %E A296443 a(8)-a(11) from _Michael S. Branicky_, Mar 31 2023