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<?php function isIBAN ($iban) { // Remove all whitespace $iban = preg_replace('/\s/', '', $iban); $iban = strtoupper($iban); if(strlen($iban) > 34) { return false; } // Create control number $alfa = str_split('ABCDEFGHIJKLMNOPQRSTUVWXYZ'); for($i = 1; $i < 27; ++$i) { $alfa_replace[] = $i + 9; } $controlNumber = str_replace($alfa, $alfa_replace, substr($iban, 4, strlen($iban)-4) . substr($iban, 0, 2) . "00"); $controlNumber = 98 - (int)bcmod($controlNumber, 97); return ((int)$controlNumber === (int)substr($iban, 2, 2)); } var_dump(isIBAN('999'));

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