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 A309738 #14 Aug 15 2019 07:28:52 %S A309738 3,7,13,31,43,73,421,2551,6481,8191,250501,4002001,64008001,81009001, %T A309738 40000200001,90000300001,64000008000001,400000000020000000001, %U A309738 3600000000060000000001,64000000000008000000000001,90000000000000300000000000001,250000000000000500000000000001 %N A309738 Primes of the form b^2*10^(2*k) + b*10^k + 1 for 1 <= b <= 9, k >= 0. %e A309738 b | Primes of the form b^2*10^(2*k) + b*10^k + 1 %e A309738 --+------------------------------------------------------------- %e A309738 1 | 3. %e A309738 2 | 7, 421, 4002001, 40000200001, 400000000020000000001, ... %e A309738 3 | 13, 90000300001, 90000000000000300000000000001, ... %e A309738 4 | %e A309738 5 | 31, 2551, 250501, 250000000000000500000000000001, ... %e A309738 6 | 43, 3600000000060000000001, ... %e A309738 7 | %e A309738 8 | 73, 6481, 64008001, 64000008000001, ... %e A309738 9 | 8191, 81009001, 810000000000000000900000000000000001, ... %Y A309738 Numbers k such that b^2*10^(2*k) + b*10^k + 1 are prime: A297422 (b=2), A306751 (b=3), A308449 (b=5), A309582 (b=6), A309719 (b=8), A309744 (b=9). %Y A309738 Cf. A309739. %K A309738 nonn,base %O A309738 1,1 %A A309738 _Seiichi Manyama_, Aug 15 2019