Read the kata's description again about what a "cubic" number is. Not a kata issue.

Hey I think one of the submitions for ruby is wrong. On the ruby submittion it says "407 407 Lucky" is the correct answer, but the cube root of 407 is 7.41. the answer thould be "Unlucky"

Thanks a lot man. You're absolutely correct. That rule is what make this kata different to his similiar kata: Step in Primes.

I don't get why people downvote your explanation. I was stuck because I didn't knew about this rule beforehand.

This question is poorly stated. To everyone trying it and are confused why your code isn't working, it's likely because of how bad this question is stated. When they ask for 2 prime numbers with a gap of g space between them, they are not asking for g=6 0 = prime 1-5 = 2 primes 3 not primes and 6 = prime. What they are asking for is that they are no primes between position 1-5 only primes at position 0 and 6.