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

var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1;
images = new Array
images[1] = "klein/31.jpg"
images[2] = "klein/32.jpg"
images[3] = "klein/33.jpg"
images[4] = "klein/34.jpg"
images[5] = "klein/35.jpg"
images[6] = "klein/36.jpg"
images[7] = "klein/37.jpg"
images[8] = "klein/38.jpg"
images[9] = "klein/39.jpg"
images[10] = "klein/40.jpg"
images[11] = "klein/41.jpg"
images[12] = "klein/42.jpg"
images[13] = "klein/43.jpg"
images[14] = "klein/44.jpg"
images[15] = "klein/45.jpg"
images[16] = "klein/46.jpg"
images[17] = "klein/47.jpg"
images[18] = "klein/48.jpg"
images[19] = "klein/49.jpg"
images[20] = "klein/50.jpg"
var image = images[rand1]
document.write('<img src="' + image + '">')