JSFiddle - React, Tailwind, and code Playground

JavaScript

var n = 21;

var a = -1;
var b = 2;
var term = 1;
var x = 0.5;
var sum = 0;
for( var i = 0; i < n; ++i ) {
    sum += term*x/(b-1);
    term *= a/b;
    x /= 4;
    a += 2;
    b += 2;    
}

var picalc = 12*sum - 1.5*Math.sqrt(3);
console.log( picalc );
console.log( Math.PI );