In PHP is really no ideal way to test large integers and determine whether they are prime numbers or not. The most popular algorithm for finding prime numbers is a memory and resource hog. It is called The Sieve of Eratosthenes.

You can get more of an idea on this method in this video and in this example from Wikipedia. He includes the full source for his solution that includes methods like isInteger, isPositive, isPerfectSquare and isPalindromicPrime. The script is also available for download.

As mainframe developers migrate from legacy systems to new languages and environments, PHP should be on the short list, said a longtime mainframe programmer who now helps others to adapt to new technologies.

The eWeek article talks about the move they think (well Darryl Taft thinks) mainframe developers should make. He even quotes Wayne Duquaine as saying that:

PHP also features a short development time. PHP scripts are five-to-10 times more productive than hand-coding a server application in Java or C from scratch, he said. And PHP also easily integrates database management system processing with HTML and XML processing.

They also comment that PHP is a good alternative to the more complex, and sometimes, more difficult languages in other LAMP-style packages.