SOURCE

var times = 0
for (var i = 1000; i <= 2000; i++) {
    if (i % 4 === 0 && i % 100 != 0 || i % 400 === 0) {
        times++;
        document.write(i + '   ')
        if (times % 4 === 0) {
            document.write(times)
            document.write("<br/>")
        }
    }
}