@AdmiralRobinson, you've asked for help on my Kata (Give me a Crazy Formula!) and I just did that. Take a look there later! Cya :)

@AdmiralRobinson, I'll help you, below is why the result is 8:

77633658797932970, middle number is odd (7), so we reduce it (second rule): 7+7+6+3+3+6+5+8(-7)+9+7+9+3+2+9+7+0 = 84

84, there isn't a middle number in it and n > 9 so we remove the last digit (first rule) => 8

So 8 is the answer.

Thanks for the feedback. Fixed!