basic ulam spiral

<style>
#out{
 font-family:monospace;
 white-space:nowrap;
 font-size: 2px;
 font-weight:bold;
 line-height:1px;
}</style>
<canvas id="cvs" width="1500" height="1500"></canvas>
<script>
window.top.primeCache = window.top.primeCache || {};
var imgSrc = "data:image/bmp;base64,Qk1EAAAAAAAAAD4AAAAoAAAAAQAAAAEAAAABAAEAAAAAAAYAAAAgLgAAIC4AAAAAAAAAAAAA////AAAAAACAAAAAAAA=";
var img = new Image();
var ctx = cvs.getContext("2d");
img.src = imgSrc;
img.onload = function(){
if(
1
){
var str = "";
 var count =2*3*5*7*11*13*17*19+1; // this is extremely interesting... change the multiples and the offset, get some strange results
var n=1,m=1,r=1;

for(var i=1; i<10000*count; i+=count,r++){
 if(isPrime(i))ctx.drawImage(img,r,n);

 if(i>=m){
    n++;
    r=1;
    m = n*n*count/2;
  }

}

}
}

function isPrime(n){
  var sq = Math.sqrt(n);
  if(Math.floor(sq)==sq){
    return false;
  }
  for(var i=2; i<sq; i++){
   if(n%i==0 && i in window.top.primeCache)return false;
 }
 window.top.primeCache[n] = true;
 return true;
}




</script>