sql>create sequence seq;

sql>select seq.nextval from emp;

 NEXTVAL
----------
         1
         2
         3
         4
         5
         6
         7
         8
         9
        10
        11
        12
        13
        14

sql>column S new_val inc;

sql>select seq.nextval S from dual;

         S
----------
        15

-----------------------
create or replace
  procedure reset_seq( p_seq_name in varchar2 )
  is
      l_val number;
  begin
      execute immediate
      'select ' || p_seq_name || '.nextval from dual' INTO l_val;

      execute immediate
      'alter sequence ' || p_seq_name || ' increment by -' || l_val ||
                                                               ' minvalue 0';

      execute immediate
      'select ' || p_seq_name || '.nextval from dual' INTO l_val;

      execute immediate
      'alter sequence ' || p_seq_name || ' increment by 1 minvalue 0';
  end;