<?php $isPrime = function($num) { for ($divider = 2; $divider < $num; $divider++) { if ($num % $divider == 0) return false; } return true; }; $primesGen = function($stop=3000) use ($isPrime) { $lastPrime = 1; while($lastPrime < $stop) { if ($isPrime(++$lastPrime)) yield $lastPrime; } }; $primes = $primesGen(); echo join(',',iterator_to_array($primes));