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 A116209 #9 Jul 18 2021 21:40:57 %S A116209 1,13,41,653,2287,2723,5491,23240971,26823191,60249661,1841968537, %T A116209 2009317771,3044234903,3258336353,8166731261,9481619237, %U A116209 1281071245505271100098621541,1551605670846640136726379653 %N A116209 Numbers k such that k concatenated with k+7 gives the product of two numbers which differ by 7. %Y A116209 Cf. A116153, A116147, A116208, A116210, A116215, A116340. %K A116209 nonn,base %O A116209 1,2 %A A116209 _Giovanni Resta_, Feb 06 2006