f :=  proc(y)
  global r;
  return r*y*(1-y/3);
end proc:

r:=2.52;

y := 2;
for i from 1 to 1 do
   y := f(y);
end do;

Digits := 50;
y := 2.0;  
for i from 1 to 55 do
   y := f(y);
end do;