JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input id="a" type="text" placeholder="a"><br>
    <input id="h" type="text" placeholder="h"><br>
    <input id="n" type="text" placeholder="n"><br>
    <input id="go" type="button" value="???"><br>
    <div id="result"></div>
</form>

JavaScript

function func(x) {
     return (x * x + 1) * Math.cos(x) * Math.cos(x);
}

function calc(fx, a, h, n) {
    var x = Number(a) + n * h;
    return (n < 1) ? func(a) + fx : calc(2 * func(x), a, h, n - 1) + fx;
}

$('#go').click(function () {
    var a = $('#a').val();
    var h = $('#h').val();
    var n = $('#n').val();
    var x = n * h + Number(a);
    $('#result').text('Result: ' + calc(func(x), a, h, n - 1));
});