One sequence for different tables

Hi,

Is it possible to create one sequence to be used for more than one table ?
Let's say I create a pkey_seq sequence.
Can I use it in table A (pkey default nextval('pkey_seq') PRIMARY KEY) and
in table B as (pkey default nextval('pkey_seq') PRIMARY KEY) ?
Is it safe in that each table will have unique values i.e. if I have a
third table C which is used to link data both from A and B using the pkey
field, will there be records having the same pkey but from different
tables?

Thanks alot
Robert