#### Fast Prime Factor Calculator

This short program is written in JavaScript and uses the techniques discussed in Project Euler Problem 3 for determining the prime factors of a composite number. Clearly, prime numbers have only themselves as a prime factor (1 is never considered prime) and are identified as such.

The input is limited to an integer less than 2^53 == 9 007 199 254 740 992

Here’s the source code, complete with the HTML, that you can paste into a file and see how it works in your favorite browser:

```
<script language="JavaScript">
//Prime Factor Calculator
function handle_enter() {
document.form.factors.value=factorsx(document.form.nx.value);
}
function factorsx(n) {
if (n < 2) { return "Neither Prime nor Composite" }
if (n > 9007199254740991) { return "Number must be less than\n 2^53 == 9 007 199 254 740 992" }
var response = n + ' = ';
message = "This Number is Prime"
var p = 2;
var np = n
while (p*p <= np) {
if (np % p == 0) {
response += p + ' x ';
np /= p;
} else p+= p>2? 2 : 1;
}
return np==n? message : response + np;
}
</script>
<center>
<table bgcolor="#dddddd">
<tr><td>
<form name="form" method="post" onSubmit="if (this.submitted){return true;} else
{ handle_enter(); return false; }">
<table>
<tr>
<td>Number to factor</td><td><input type="text" size=14 name="nx">
<input type="button" value="Click here for factors"
onClick="form.factors.value=factorsx(form.nx.value)"></tr>
<tr>
<td style="vertical-align: top">Prime factors</td>
<td><textarea name="factors" rows=2 cols=40></textarea></td><td> </td></tr>
</table>
</form>
</td></tr></table>
</center>
```

prime factor calculator v 1.1

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[…] factor, which is nice, because it is, in fact, itself the largest prime factor. Here’s a Javascript prime factor calculator to find all the prime factors of a […]