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 A115543 #7 Jul 15 2021 09:15:25 %S A115543 1,20408163265306122448979591836734694, %T A115543 81632653061224489795918367346938776, %U A115543 20408163265306122448979591836734693877551020408163265306122448979591836734694 %N A115543 Numbers k such that the concatenation of k with 6*k gives a square. %e A115543 1_6 = 4^2. %Y A115543 Cf. A102567, A106497, A115527 - A115556. %K A115543 nonn,base,less %O A115543 1,2 %A A115543 _Giovanni Resta_, Jan 25 2006