Factorising

[Anon]

Okay i need to find all the factors of a number and then put them into an array. I looked about in the manual and couldn't see a factorising function.

So i tried dividing a number by another and seeing if the result is a integar. But i havn't been able to code this successfully. Could anyone suggest some code to factorise a number. I would be greatful for any help.

Thanks

[Anon]

this is generally a hard thing to do (very processor intensive), that is why encryption is based on this principle...

check the code in any popular encryption breaking utility (password cracker, etc)

[timbach2]

To get a factorial, you have to find it recursively. In this example, functions factors() and listFactors() are just FYI.

<?php

function factorial($number) {
global $factorial;
$factorial[0]=1;
for($i=2;($number/$i)<>round($number/$i);$i++) {
// increments $i until a factor is found.
}

$factorial[]=$i;
if(($number/$i)>2) {
factorial($number/$i);
}

}

function factors($number) {
global $factors;
for($i=1;$i<=($number/2);$i++) {
if($number/$i==round($number/$i)) {
$factors[$i]=($number/$i);
}
}
}

function listFactors($factors) {
while(list($key,$value)=each($factors)) {
print "($key,$value)<br>";
}
}

$number=1000;

factors($number);
listFactors($factors);

print "<hr>";
factorial($number);
listFactors($factorial);

?>