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ulamSpiral-0.html
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<!DOCTYPE html>
<html>
<head>
<style>
#wrapper {
position: relative;
}
.number {
position: absolute;
width: 16px;
height: 16px;
line-height: 16px;
font-size: 7px;
text-align: center;
color: #e1e1e1;
border-radius: 10px;
}
.prime {
color: #000;
font-weight: bold;
background-color: #E1E1E1;
}
.first {
background-color: red;
}
</style>
<title>ulamSpiral-0</title>
</head>
<body>
<div id="wrapper"></div>
<script>
// Returns TRUE if `n` is a prime
var isPrime = function (n) {
var i, l;
// 1 is not a prime
if (n === 1) {
return false;
}
// 2 is a prime - but also an even number
if (n === 2) {
return true;
}
// Even numbers greater than 2 are not primes
if (n % 2 === 0) {
return false;
}
// Checking for divisors
for (i = 3, l = Math.sqrt(n); i <= l; i += 2) {
if (n % i === 0) {
return false;
}
}
// If no divisors was found we have a prime
return true;
};
// Append an element to the DOM
var appendNum = (function () {
var doc = document;
var wrapper = document.getElementById('wrapper');
var first = true;
return function (num, highlight, x, y) {
var div = doc.createElement('div');
var className = 'number';
className += highlight ? ' prime' : '';
className += first ? ' first' : '';
first = false;
div.className = className;
div.style.left = x + 'px';
div.style.top = y + 'px';
//div.appendChild(doc.createTextNode(i));
wrapper.appendChild(div);
};
} ());
// Position
var size = 16;
var offsetX = 400;
var offsetY = 350;
var dir = 0; // 0 = right, 1 = up, 2 = left, 3 = down
var limit = 1; // Amount to print before changing direction
var counter = 0; // How many printed in the current directio
var turns = 0; // Counter for turns taken, every second; limit++
for (var i = 1; i < 2000; i++) {
appendNum(i, isPrime(i), offsetX, offsetY);
switch (dir) {
case 0 :
offsetX += size;
break;
case 1 :
offsetY -= size;
break;
case 2 :
offsetX -= size;
break;
case 3 :
offsetY += size;
break;
}
counter++;
if (counter >= limit) {
counter = 0;
turns = (turns + 1) % 2;
dir = (dir + 1) % 4;
if (turns === 0) {
limit++;
}
}
}
</script>
</body>
</html>