[emirp]

I can think of a couple of things off the top of my head:

- You can reject numbers that start with 2,4,5,6 or 8 since their reverse won't be prime.

- If you're searching through a range of numbers for emirps avoid checking for the same pair twice. For example if you start at 1 and check for emirps, by the time you're checking 311 you've already checked 113 so you don't need to check 311.