The HiCalc HD Pro calculator app is currently free and supports a wide variety of functions including statistical en equation solving.
HiCalc HD PRO screenshot
Calculator Easy HD is a free calculator app for the iPhone and iPad which also lists your previous calculations.
Screenshot in landscape mode
I have several delegated calendars setup in my Google account. Unfortunately my iPad only syncs with my primary calendar and there is no way to select my delegated calendars. Then I found this page. Which describes how to solve this problem. The answer is simple just visit https://www.google.com/calendar/iphoneselect and check the calendars you want to sync. Restart the calendar app and all calendars are synced. You might have to check them in the view options when they do not show up.