PHP implementation of narcissus number code sharing

The so-called narcissus number is a number raised to a power, also known as Armstrong number. It is also known as narcissus number among the people. In fact, only 3-digit exponentiates are narcissus numbers. 4 digits, 5 digits, 6 digits, etc. have different names.

Example, PHP code to implement narcissus number.

//Armstrong number: a k-digit number, the sum of the k-th power of the numbers in each digit is equal to itself. (Example: 1^3 + 5^3 + 3^3 = 153)
class Armstrong {
 static function index(){
 for ( $i = 100; $i < 100000; $i++ ) {
 echo self: :is_armstrong($i) ? $i . '' : '';
 }
 } // edit by bbs.it-home.org
 static function is_armstrong($num){
 $s = 0;
 $k = strlen($num);
 $d = str_split($num);
 foreach ($d as $r) {
 $s += bcpow($r, $k);
 }
 return $num == $s;
 }
}
Armstrong::index();