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 A261510 #20 Aug 25 2016 21:42:09 %S A261510 1111211111,1111411111,3333133333,9999499999, %T A261510 1111111111112111111111111111,1111311331137311333311111111, %U A261510 1111411441142411444411111111,1111611661167611666611111111,1111811881185811888811111111,3333033003305033000033333333,3333133113312133111133333333 %N A261510 Triangle-congruent primes greater than 10 with a single digit at the center. %C A261510 Subsequence of A050758. %H A261510 G. L. Honaker, Jr. and C. Caldwell, <a href="https://primes.utm.edu/curios/page.php?number_id=7464">1111211111</a> %e A261510 a(6) can be represented as follows: %e A261510 ......1 %e A261510 .....1 1 %e A261510 ....1 3 1 %e A261510 ...1 3 3 1 %e A261510 ..1 3 7 3 1 %e A261510 .1 3 3 3 3 1 %e A261510 1 1 1 1 1 1 1 %Y A261510 Cf. A050758. %K A261510 nonn,base %O A261510 1,1 %A A261510 _Felix Fröhlich_, Aug 22 2015