Finding WordPress Administrator User IDs

admins-ids.php

<?php
function get_admins_user_ids(){
	global $wpdb;
	//Select all users ID
    $all_users = $wpdb->get_col("SELECT ID FROM $wpdb->users ORDER BY ID");
    $adminsArray = array();
    foreach ( $all_users as $uid ) {
		//Get all users that have administrator role
        if(get_userdata($uid)->roles[0] == 'administrator'){
            $adminsArray[] = $uid;
        }
    }
    return $adminsArray;
}