function ccc13(form) {

  factor = 3;
  sum = 0;

  for (index = form.numero.value.length; index > 0; --index) {

    sum = sum + form.numero.value.substring (index-1, index) * factor;
    factor = 4 - factor;
  }

   cc = ((1000 - sum) % 10);

   form.chiffre.value = "0" + form.numero.value + cc;

   result = form.chiffre.value;

   form.cc.value = cc;

  if (form.numero.value.length!=12){
	alert("Vinsamlegast sláið inn 12 tölur")
	form.cc.value = ""
      form.chiffre.value = "";
   }
}

function ccc8(form) {
  factor = 3;
  sum = 0;

  for (index = form.numero.value.length; index > 0; --index) {
    sum = sum + form.numero.value.substring (index-1, index) * factor;

    factor = 4 - factor;

  }

   cc = ((1000 - sum) % 10);

   form.chiffre.value = "000000" + form.numero.value + cc;

   result = form.chiffre.value;
   form.cc.value = cc

  if (form.numero.value.length!=7){

	alert("Vinsamlegast sláið inn 7 tölur")

	form.cc.value = ""

      form.chiffre.value = "";

   }

}

function ccc12(form) {

  factor = 3;

  sum = 0;

  for (index = form.numero.value.length; index > 0; --index) {

    sum = sum + form.numero.value.substring (index-1, index) * factor;

    factor = 4 - factor;

  }

   cc = ((1000 - sum) % 10);

   form.chiffre.value = "00" + form.numero.value + cc;

   result = form.chiffre.value;

   form.cc.value = cc

  if (form.numero.value.length!=11){

	alert("Vinsamlegast sláið inn 11 tölur")

	form.cc.value = ""

      form.chiffre.value = "";

   }

}

function ccc14(form) {

  factor = 3;
  sum = 0;

  for (index = form.numero.value.length; index > 0; --index) {
    sum = sum + form.numero.value.substring (index-1, index) * factor;

    factor = 4 - factor;
  }

   cc = ((1000 - sum) % 10);

   form.chiffre.value = form.numero.value + cc;
   result = form.chiffre.value;

  form.cc.value = cc

  if (form.numero.value.length!=13){

	alert("Vinsamlegast sláið inn 13 tölur")

	form.cc.value = ""

      form.chiffre.value = "";
   }

}

function ccc18(form) {

  factor = 3;

  sum = 0;

  for (index = form.numero.value.length; index > 0; --index) {

    sum = sum + form.numero.value.substring (index-1, index) * factor;

    factor = 4 - factor;
  }

   cc = ((1000 - sum) % 10);

   form.cc.value = cc

  if (form.numero.value.length!=17){

	alert("Vinsamlegast sláið inn 17 tölur")

	form.cc.value = "";
   }
}






 function NumberFilter(evt)
      {
         var charCode = (evt.which) ? evt.which : event.keyCode
         if (charCode > 31 && (charCode < 48 || charCode > 57))
            return false;

         return true;
      }