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 A111988 #5 Aug 05 2021 18:22:25
%S A111988 1,4,8,16,0,24,32,48,40,19,27,80,0,96,29,144,0,120,37,76,160,108,128,
%T A111988 240,0,0,136,288,0,152,81,336,216,67,0,360,73,148,0,304,0,480,0,432,
%U A111988 232,384,0,720,416,0,101,103,125,440,109,672,296,0,0,464,0,324,544,1008,0
%N A111988 Greatest number having n quadratic residues, or 0 if there is no such number.
%e A111988 a(4)=16 because, of the five numbers having 4 quadratic residues (6,7,9,12,16), the greatest is 16.
%t A111988 t=Table[Length[Union[Mod[Range[0, n/2]^2, n]]], {n, 10000}]; Table[pos=Flatten[Position[t, n]]; If[Length[pos]==0, 0, Last[pos]], {n, 100}]
%Y A111988 Cf. A037046 (n such that a(n)=0), A111986 (number of numbers having n quadratic residues), A111987 (least number having n quadratic residues).
%K A111988 nonn
%O A111988 1,2
%A A111988 _T. D. Noe_, Aug 25 2005