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<?php function isPrime($num) { for ($i = 2; $i < $num; $i++) { if ($num % $i == 0) { return false; } } return true; } function firstAndLastDigitEqual($num, $digit) { return substr($num, 0, 1) == (string)$digit && substr($num, -1) == (string)$digit; } $foundPrimes = 0; for ($i = 1; true; $i++) { if (firstAndLastDigitEqual($i, 3) && isPrime($i)) { if (++$foundPrimes == 333) { echo $i; break; } } }

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30.96 ms | 402 KiB | 5 Q