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

         return true;
      }

function a1()
{
var n = document.form1.n.value;
var a = document.form1.a.value;
var d = document.form1.d.value;
if((n=="" && a=="" && d=="")||(n=="" ||a==""||d==""))
{
alert("please enter all the values");
}
else
{
var f = n-1;
var e = Math.pow( d,f);
document.form1.gp.value=a*e;
}
}