today=new Date(); 
jran=today.getTime(); 
function rnd() { 
ia=9301; 
ic=49297; 
im=233280; 
jran = (jran*ia+ic) % im; 
return jran/(im*1.0); 
}; 
function rand(number) { 
return Math.ceil(rnd()*number); 
}; 
document.write("<center>"); 
for(i=1;i<=1;i++) { 
myNum=(rand(5));
if(myNum == 1) document.write("<img src='images/a_1.jpg'>");
if(myNum == 2) document.write("<img src='images/a_2.jpg'>");  
if(myNum == 3) document.write("<img src='images/a_3.jpg'>"); 
if(myNum == 4) document.write("<img src='images/a_4.jpg'>");  
if(myNum == 5) document.write("<img src='images/a_5.jpg'>");   
else { 
document.write(); 
} 
}; 
document.write("</center>");