function swap() {
var numfindings=19;
rndfind = new Array("a001", "a002", "a003","a004","a005","a006","a007","a008","a009","a010","a011","a012","a013","a014","a015","a016","a017","a018","a019"); 
x=(Math.floor(Math.random()*numfindings));
randomfinding=(rndfind[x]);
document.getElementById(randomfinding).style.display = "block"; 
}

if (document.getElementById) { 
addOnLoadFunction(swap);
};