function calculate( form )
{
   var num = parseInt( form.number.value );

   if ( isNaN( num ) || num < 0 )
   {
      form.result.value = ( form.number.value + " ?");
   }

   if ( num == 1 || num == 2 )
   {
      form.result.value = ( num + " !" );
   }

   for ( var i = 2; i < num; i++ )
   {
      if ( num % i == 0 )
      {
         var prime = "yes";

         form.result.value = ( i + "..." );
         break;
      }

      if ( num % i != 0 ) var prime = "no";
   }

   if ( prime == "no" ) form.result.value = ( num + " !" );
}