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 A115527 #11 Jul 15 2021 06:26:55 %S A115527 3,8163265306122448979592,18367346938775510204082, %T A115527 32653061224489795918368, %U A115527 504986744097967428355005681100871102133568993813912384800 %N A115527 Numbers k such that the concatenation of k with 2*k gives a square. %e A115527 3_6 = 6^2. %Y A115527 Cf. A102567, A106497, A115528 - A115556. %K A115527 nonn,base %O A115527 1,1 %A A115527 _Giovanni Resta_, Jan 25 2006