Problem with complex outer join expression

I'm using 7.4.5 on win XP Pro SP1.

I'm getting:-

ERROR: syntax error at or near "(" at character 155

from the query:-

select dummy_records.sequence_nr,timesheets.weekending,timesheets.timesheet_id
from dummy_records
,left outer join timesheets
on (timesheets.weekending = ('2006-04-09' + (integer
dummy_records.sequence_nr-1)*7)))
where dummy_records.sequence_nr between 1 and (date '2006-04-23' -
date '2006-04-09')/7+1;

What this query is trying to achieve is:-

Find all weekending dates between 2 given weekending dates and any
corresponding timesheets for those weekending dates.

What am I doing wrong here? How do I achieve what I want?

Chris
--
Chris Velevitch
Manager - Sydney Flash Platform Developers Group
www.flashdev.org.au