drop sequence

1DECLARE
2    s_exist NUMBER(1);
3BEGIN
4    SELECT CASE WHEN exists(SELECT * FROM ALL_SEQUENCES 
5                           WHERE SEQUENCE_NAME = 'seq_name') THEN 1
6       	ELSE 0 
7    END INTO s_exist FROM DUAL;
8    IF s_exist = 1 THEN
9        EXECUTE IMMEDIATE 'DROP SEQUENCE seq_name';
10    END IF;
11END;