var oTab13_7_2 = document.getElementById('tab13_7');
    var oBtn13_7_2 = document.getElementById('btn13_7');

    oBtn13_7_2.onclick = function () 
    {
        var arr = [];
        for (var i = 0; i < oTab13_7_2.tBodies[0].rows.length; i++) 
        {
            arr[i] = oTab13_7_2.tBodies[0].rows[i];
        }

        arr.sort(function (tr1, tr2) 
        {
            var n1 = parseInt(tr1.cells[0].innerHTML);
            var n2 = parseInt(tr2.cells[0].innerHTML);
            return n1 - n2;
        });
        //When the sort() function compares two values, it sends the values to the compare function, and sorts the values
        according to the returned (negative, zero, positive) value.

        for (var i = 0; i < arr.length; i++) 
        {
            oTab13_7_2.tBodies[0].appendChild(arr[i]);
        }
    };