(*  format the decimal portion of a number  *)

  (*  display normal precision  *)
Print(N(Pi));

  (*  calculate a specified precision, approx. 104,348/33,215  *)
x = N(
 3943771611212266962743738812600748213157266596588744951727393497446921245353005283
 /
 1255341492699841451528811722575401081588363886480089431843026103930863337221076748
 , 152);
  (*  convert it to a string()  *)
str = ToString(x);
(*  Symja appends string length  *)
str = StringTake(str, StringPosition(str, "`", 1)[[1, 1]] - 1 );
  (*  find the .  *)
dotPos = Part(StringPosition(str, "."), 1, 1);
  (*  insert a space every thousands-th position  *)
For(k=StringLength(str), k >= dotPos+2, k--,
  If(Mod(k-dotPos, 3) == 0, str = StringInsert(str, " ", k))
);

str