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<?php $count = 0; function is_prime($n) { for ($i = 2; $i < sqrt($n); $i++) { if ($n % $i == 0) { return false; } } return true; } for ($i = 20000; $i <= 40000; $i++) { if (substr_count($i, '9') == 2) { if (is_prime($i)) { $count++; } } } echo 'answer: ', $count, "\n";
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