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prime.html
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<!DOCTYPE html>
<html lang="en">
<!-- See: https://rtestardi.github.io/pages/prime.html -->
<body>
<canvas id="canvas" width=512 height=256></canvas>
<p>Max:<input id='max' onchange="GraphPrimes()">
<p id=details>
<script>
'use strict';
var ctx;
function drawpoint(x, y)
{
ctx.beginPath();
ctx.arc(Math.trunc(x), Math.trunc(y), 2, 0, 2*Math.PI, false);
ctx.fill();
}
function isprime(n)
{
var i;
for (i = 2; i < Math.trunc(Math.sqrt(n)+1); i++) {
if (n%i == 0) {
return false;
}
}
return true;
}
function GraphPrimes()
{
var i;
var n;
var max = Number(document.getElementById('max').value);
ctx = document.getElementById('canvas').getContext('2d');
n = 0;
var points = [];
for (i = 0; i < max; i++) {
if (isprime(i)) {
n++;
}
if (i%(Math.trunc((max+511)/512)) == 0) {
points.push({x: i, y: n});
}
}
// i is our max x value and n is our max y value; scale the graph
var j;
for (j = 0; j < points.length; j++) {
drawpoint(points[j].x*512/i, 256-points[j].y*256/n);
}
document.getElementById('details').innerHTML = "max = " + max + " n = " + n + " max/n = " + max/n;
}
</script>
</body>
</html>