Linq with "not in" and "Count" query

I want a query like 

select count(*) from Table1 where Id not in (Select Id from Table2)

select count(*) from Table1  where Id in (Select Id from Table2)

These in Linq .

I have checked with Contains but i t  gives me runtime error 

var ss = (from reg in db.Table1  where !db.Table2.Contains(reg) select reg).Count();

Please suggest