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 A115535 #10 Jul 22 2021 07:50:55 %S A115535 25721,28836,32129,35600,39249,43076,47081,51264,55625,60164,64881, %T A115535 69776,74849,80100,85529,91136,96921,102884,109025,115344,121841, %U A115535 128516,135369,142400,149609,156996,164561,172304,180225,188324,196601,205056 %N A115535 Numbers k such that the concatenation of k with 4*k gives a square. %C A115535 Not the same as P(n) = 89*n^2 + 2848*n + 22784: P(n) = a(n) for a < 37, but a(37) = 3698225. - _Charles R Greathouse IV_, Jul 28 2010 %e A115535 25721_102884 = 160378^2. %t A115535 Select[Range[250000],IntegerQ[Sqrt[#*10^IntegerLength[4*#]+4*#]]&] (* _Harvey P. Dale_, Jan 04 2019 *) %Y A115535 Cf. A102567, A106497, A115527 - A115556. %K A115535 nonn,base %O A115535 1,1 %A A115535 _Giovanni Resta_, Jan 25 2006