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Title : Prime Spiral is a image plotted with all the primes in a number spiral.
Categories : Algorithms, Graphics, GD image library, Math. Click here to Update Your Picture
Chao Xu
Date : May 15th 2007
Grade : 2 of 5 (graded 1 times)
Viewed : 909
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Made by Chao Xu (WebDevLogs.com)
You need a prime counting function, it can be finded here :
http://www.weberdev.com/get_example-4635.html

<?php
$size
= 500;
$prime = esprime($size*$size);
$image = imagecreate($size,$size);
imagecolorallocate($image,255,255,255);
$color = imagecolorallocate($image,0,0,0);
$size2=$size/2;

$n = 2;$t = true;$sn=4;

$midu=2;$midl=4;$midd=6;$midr=8;

$i = 0;
while(
$n<$size){
        if(
$prime[$i]<=$sn){
               
$p = $prime[$i++];
                if(
$t){//even
                       
if($p <= $sn-$n){
                               
$x = $n/2;
                               
$y = $midu - $p;
                        }else{
                               
$x = $midl -$p;
                               
$y = -$n/2;
                        }
                }else{
//odd
                       
if($p <= $sn-$n){
                               
$x = (-$n/2)+0.5;
                               
$y = $p - $midd;
                        }else{
                               
$x = $p - $midr;
                               
$y = ($n/2)-0.5;
                        }
                }
               
imagesetpixel($image,$x+$size2,$y+$size2,$color);
        }else{
                ++
$n;
               
$sn = $n * $n;
               
$t = !$t;
                if(
$t){
                       
$midu = $sn-$n*1.5+1;
                       
$midl = $sn-$n*0.5+1;
                       
                }else{
                       
$midd = $sn-$n*1.5+1.5;
                       
$midr = $sn-$n*0.5+0.5;
                }
        }
}
header("Content-type: image/png");
imagepng($image);
?>



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