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 A309739 #22 Aug 15 2019 07:28:59 %S A309739 3,5,7,11,13,17,19,331,661,881,991,20201,60601,90901,2002001,5005001, %T A309739 300030001,600060001,50000500001,2000002000001,8000008000001, %U A309739 9000009000001,3000000003000000001,200000000020000000001,80000000000800000000001 %N A309739 Primes of the form b*10^(2*k) + b*10^k + 1 for 1 <= b <= 9, k >= 0. %e A309739 b | Primes of the form b*10^(2*k) + b*10^k + 1 %e A309739 --+------------------------------------------------------------- %e A309739 1 | 3. %e A309739 2 | 5, 20201, 2002001, 2000002000001, 200000000020000000001, ... %e A309739 3 | 7, 331, 300030001, 3000000003000000001. %e A309739 4 | %e A309739 5 | 11, 5005001, 50000500001, ... %e A309739 6 | 13, 661, 60601, 600060001, ... %e A309739 7 | %e A309739 8 | 17, 881, 8000008000001, 80000000000800000000001, ... %e A309739 9 | 19, 991, 90901, 9000009000001, 9000000000009000000000001, ... %Y A309739 Numbers k such that b*10^(2*k) + b*10^k + 1 are prime: A296444 (b=2), A309740 (b=5), A309741 (b=6), A309742 (b=8), A309743 (b=9). %Y A309739 Primes of the form b*10^(2*k) + b*10^k + 1: A160432 (b=3). %Y A309739 Cf. A309738. %K A309739 nonn,base %O A309739 1,1 %A A309739 _Seiichi Manyama_, Aug 15 2019