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 A023111 #36 Feb 12 2021 06:41:03
%S A023111 0,36,51984,74960964,108093658176,155870980128900,224765845252215696,
%T A023111 324112192982714904804,467369557515229640511744,
%U A023111 673946577824768158903030116,971830497853758169908528915600,1401378903958541456239939793265156,2020787407677718926139823273359439424
%N A023111 Squares that remain square when the digit 1 is appended.
%C A023111 The terms of the sequence are the squares of the y-values in the solution to the Pellian equation x^2-10*y^2=1. - _Colin Barker_, Sep 28 2013
%C A023111 After 0, the sequence lists the numbers k for which A055437(k) is a perfect square. - _Bruno Berselli_, Jan 16 2018
%H A023111 Colin Barker, <a href="/A023111/b023111.txt">Table of n, a(n) for n = 1..300</a>
%H A023111 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1443,-1443,1).
%F A023111 G.f.: 36*x^2*(1 + x) / ((1 - x)*(1 - 1442*x + x^2)). - _Colin Barker_, Jan 31 2013
%F A023111 a(0)=0, a(1)=36, a(2)=51984, a(n) = 1443*a(n-1)-1443*a(n-2)+a(n-3). - _Harvey P. Dale_, Dec 23 2013
%F A023111 a(n) = (721 + 228*sqrt(10))^(-n)*(721+228*sqrt(10) - 2*(721+228*sqrt(10))^n + (721-228*sqrt(10))*(721+228*sqrt(10))^(2*n)) / 40. - _Colin Barker_, Dec 29 2017
%e A023111 36 is a term because both 36 and 361 are squares.
%t A023111 LinearRecurrence[{1443,-1443,1},{0,36,51984},20] (* _Harvey P. Dale_, Dec 23 2013 *)
%o A023111 (PARI) concat(0, Vec(36*x^2*(1 + x) / ((1 - x)*(1 - 1442*x + x^2)) + O(x^15))) \\ _Colin Barker_, Dec 29 2017
%Y A023111 Cf. A023110.
%K A023111 nonn,base,easy
%O A023111 1,2
%A A023111 _David W. Wilson_