var imagenumber = 20;
var randomnumber = Math.random();

var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1;
images = new Array
images[1] = "klein/1.jpg"
images[2] = "klein/2.jpg"
images[3] = "klein/3.jpg"
images[4] = "klein/4.jpg"
images[5] = "klein/5.jpg"
images[6] = "klein/6.jpg"
images[7] = "klein/7.jpg"
images[8] = "klein/8.jpg"
images[9] = "klein/9.jpg"
images[10] = "klein/10.jpg"
images[11] = "klein/11.jpg"
images[12] = "klein/12.jpg"
images[13] = "klein/13.jpg"
images[14] = "klein/14.jpg"
images[15] = "klein/15.jpg"
images[16] = "klein/16.jpg"
images[17] = "klein/17.jpg"
images[18] = "klein/18.jpg"
images[19] = "klein/19.jpg"
images[20] = "klein/20.jpg"
var image = images[rand1]
document.write('<img src="' + image + '">')