SQL & PL/SQL

There is a schema say 'A' in which there is a package called 'B' in which this is a funtcion (below). In this function 'TIMESTMAP' is used which while compiling in 11g is giving error. I want to create a public synonym for TIMESTAMP. Can anyone please provide me the script for the same.
FUNCTION generate_random_number
Return Number
IS
l_seq_no VARCHA2(6)
l_sys_date CHAR(10)
BEGIN
SELECT LTRIM(TO_CHAR(TIMESTAMP.NEXTVAL,'000000'), ' ')
INTO l_seq_no
from DUAL;

SELECT TO_CHAR(SYSDATE, 'H24:MI:SS')
INTO l_sys_date
from DUAL