psql> CREATE SEQUENCE foo;
psql> CREATE TABLE bar (
  id     char(10) PRIMARY KEY DEFAULT 'bar_' || nextval('foo')
, name   text
);
psql> INSERT INTO bar (name) VALUES ('Alice');
psql> INSERT INTO bar (name) VALUES ('Bob');
psql> SELECT * FROM bar;
     id     | name
------------+-------
 bar_1      | Alice
 bar_2      | Bob