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 A273868 #10 Jun 13 2022 02:26:06 %S A273868 25,51,91,107,145,651,1473,2145,5577,12457 %N A273868 Numbers k such that 10^k - 9^(k+1) is prime. %C A273868 a(11) > 10^5. %e A273868 25 is a term since 10^25 - 9^26 = 3538918110773326701067759, which is a prime number. %t A273868 Select[Range[21, 100000], PrimeQ[10^# - 9^(# + 1)] &] %o A273868 (PARI) is(n)=ispseudoprime(10^n-9^(n+1)) \\ _Charles R Greathouse IV_, Jun 08 2016 %Y A273868 Cf. A093713, A082103, A093717, A093793, A096185, A093794, A093795, A096186, A271883. %K A273868 nonn,more %O A273868 1,1 %A A273868 _Robert Price_, Jun 01 2016