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 A364644 #13 Jan 27 2024 15:56:58 %S A364644 7,25,355,823 %N A364644 Numbers k such that floor(10^k/7) is prime. %C A364644 Numbers k such that A090519(k) = 7. %C A364644 All terms == 1 (mod 6). %C A364644 Numbers k such that (10^k-3)/7 is prime. %C A364644 a(5) > 20000 if it exists. - _Hugo Pfoertner_, Jul 31 2023 %e A364644 a(1) = 7 is a term because floor(10^7/7) = 1428571 is prime. %p A364644 select(n -> isprime(floor(10^n/7)),[seq(i,i=1..1000,6)]); %Y A364644 Cf. A090519. %K A364644 nonn,more,hard %O A364644 1,1 %A A364644 _Robert Israel_, Jul 31 2023