Check Oracle run Cluster Mode or not

SET SERVEROUT ON

DECLARE
BEGIN
    IF DBMS_UTILITY.is_cluster_database
    THEN
        DBMS_OUTPUT.put_line (
            'Your database is running in Parallel server mode');
    ELSE
        DBMS_OUTPUT.put_line (
            'Your database is NOT running in Parallel server mode');
    END IF;
END;