I had this same issue and tracked down the problem. I had assumed that steps had to be between adjacent primes, but that is not the case.

A note on my own answer: I got lucky that this actually worked. I made a mistake in that Enum.find/2 should have been Enum.any?/2.

I see a lot of devs using String.graphemes, which is probably smarter if you're dealing with unicode characters, emojis, etc... The requirements in this test are simply strings a-z, so this does actually satisfy the requirement.