calculate_pi.js

var factorial = function(n) {
	++n;
	var r = 1;
  while(n-->1)
  	r*=n;
   return r;
}

var calculatePI = function(n) {
	n = n || 30;
	var k = Math.sqrt(2)*2/9801;
  var sum = 0;
  for(var i=0; i<n; i++) {
  	sum += (factorial(4*i)*(1103+26390*i))/
    (Math.pow(factorial(i), 4)*Math.pow(396, 4*i));
  }
  return 1/(sum*k)
}