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 A306751 #41 Sep 05 2024 10:16:22 %S A306751 0,5,14,77,104,2603,2657,24029 %N A306751 Numbers k such that 9*10^(2*k) + 3*10^k + 1 is prime. %e A306751 13 is prime ==> a(1) = 0. %e A306751 931 = 7^2 * 19. %e A306751 90301 = 73 * 1237. %e A306751 9003001 = 7 * 757 * 1699. %e A306751 900030001 = 13 * 4969 * 13933. %e A306751 90000300001 is prime ==> a(2) = 5. %o A306751 (PARI) for(k=0, 1e3, if(ispseudoprime(9*100^k+3*10^k+1), print1(k", "))) %Y A306751 Cf. A309738, A309743. %K A306751 nonn,base,more %O A306751 1,2 %A A306751 _Seiichi Manyama_, Aug 15 2019 %E A306751 a(8) from _Michael S. Branicky_, Sep 05 2024