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 A115537 #6 Jul 15 2021 09:17:09 %S A115537 17728531856,27700831025,39889196676,54293628809,70914127424, %T A115537 89750692521,32653061224489796,73469387755102041, %U A115537 1245674740484429065743944636678200692041522491349481 %N A115537 Numbers k such that the concatenation of 4*k with k gives a square. %e A115537 70914127424_17728531856 = 84210526316^2. %Y A115537 Cf. A102567, A106497, A115527 - A115556. %K A115537 nonn,base %O A115537 1,1 %A A115537 _Giovanni Resta_, Jan 25 2006