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 A296444 #38 May 01 2025 13:24:03 %S A296444 0,2,3,6,10,276,746,1090,1485,6186,8571,15594 %N A296444 Numbers k such that 2*10^(2k) + 2*10^k + 1 are prime. %C A296444 Numbers of this form divide 4*10^(4k)+1. %C A296444 a(13) > 20000. - _Michael S. Branicky_, May 01 2025 %e A296444 5, 20201, 2002001, 2000002000001, and 200000000020000000001 are prime, while 221=13*17, 200020001=569*351529, and 20000200001=17*29*1129*35933. %t A296444 ParallelMap[ If[ PrimeQ[2*10^(2 #) + 2*10^# + 1], #, Nothing] &, Range@ 6500] (* _Robert G. Wilson v_, Dec 13 2017 *) %o A296444 (PARI) isok(k) = isprime(2*10^(2*k)+2*10^k+1); \\ _Michel Marcus_, Dec 13 2017 %Y A296444 See A296443 for 2*10^(2k)-2*10^k+1. %Y A296444 Cf. A297422, A309739. %K A296444 nonn,more %O A296444 1,2 %A A296444 _Patrick A. Thomas_, Dec 13 2017 %E A296444 a(6)-a(7) from _Michel Marcus_, Dec 13 2017 %E A296444 a(8)-a(10) from _Robert G. Wilson v_, Dec 13 2017 %E A296444 a(1) = 0 inserted by _Seiichi Manyama_, Aug 15 2019 %E A296444 a(11) from _Michael S. Branicky_, Apr 16 2023 %E A296444 a(12) from _Michael S. Branicky_, Apr 30 2025