Haha! No, I can't add 0s. If I could, then I'd simply do 5+7+7+4+0!+0!+0!+0!+0!.... etc.

I like your other solutions! I hadn't known floor and ceiling functions had symbols. I'm a little afraid to use them - I think I'm pushing it just having used factorials - but I'll list it for now, and replace it if I can find anything 'simpler'.

In the meantime, I'm only missing two of the numbers between 55-69.