max = 2200;
maxsq = max^2;
d = Range[max]^2;
Dynamic[{a, b, Length[d]}]
Do[
 Do[
  c = Range[1, Floor[(maxsq - a^2 - b^2)^(1/2)]];
  dposs = a^2 + b^2 + c^2;
  d = Complement[d, dposs]
  ,
  {b, Floor[(maxsq - a^2)^(1/2)]}
  ]
 ,
 {a, Floor[maxsq^(1/2)]}
 ]
Sqrt[d]