[ruslan_mart]

Экпирементируйте

var ch = <?=$i?>,
	prev,
	rand = function() {
		var n = Math.floor(Math.random() * ch) + 1;
		return n == prev ? rand() : (prev = n);
	};

$('#btn-rnd').click(function() {
	var n = rand();
	$('#tab-' + n).fadeOut(500, function() {
		$(this).load('fun-' + n + '.php').fadeIn(500);
	});
});