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 A115553 #6 Jul 15 2021 09:13:16 %S A115553 2041,8164,2366863905325444,5325443786982249,9467455621301776, %T A115553 2040816326530612244897959183673469387755102041, %U A115553 8163265306122448979591836734693877551020408164 %N A115553 Numbers k such that the concatenation of k with 9*k gives a square. %e A115553 2041_18369 = 14287^2. %Y A115553 Cf. A102567, A106497, A115527 - A115556. %K A115553 nonn,base %O A115553 1,1 %A A115553 _Giovanni Resta_, Jan 25 2006