CREATE OR REPLACE FUNCTION add_entry(_user_name text)
  RETURNS bigint AS
$BODY$
  DECLARE
    user_name text := '#' || $1;
    user_id bigint;
  BEGIN

    -- get the ID from the sequence
    SELECT nextval('my_sequence') INTO user_id;

    -- insert the name (and some other data not shown here) 5x
    FOR item IN 1..5
    LOOP
      INSERT INTO mytable
        (id,index,username)
        VALUES (user_id,item,user_name);
    END LOOP;

    -- send notify that an insertion took place
    notify my_notify;

    RETURN id;
  END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;

select * from mytable where id = (select add_entry('MyTestUser'));