function CheckPrime(Number: Cardinal): boolean; 
var i: Cardinal; 
begin 
  result := false; 
  if Number < 3 then exit; 
  for i := 2 to trunc(sqrt(Number) + 1) do 
    if frac(Number / i) = 0.0 then exit; 
  result := true; 
end; 
 
 
// Beispielaufruf 
 
procedure TForm1.Button1Click(Sender: TObject); 
begin 
  if CheckPrime(4294967291) then showmessage('Primzahl') 
  else showmessage('Keine Primzahl'); 
end;