Check Prime Numbers

function IsPrime(ANumber: Cardinal): Boolean;
var
  DivCount: Integer;
  Divisor: Cardinal;
begin
  DivCount := 0;
  if (ANumber > 0) then
  begin
    for Divisor := 1 to ANumber do
    begin
      if (ANumber mod Divisor) = 0 then
        Inc(DivCount);
      if (DivCount > 2) then
        Break;
    end;
  end;
  Result := (DivCount = 2);
end;

Beispiel :

procedure TForm1.Button1Click(Sender: TObject);
begin
   if IsPrime(4) then
    ShowMessage('prim')
  else
    ShowMessage('nicht prim');
end;