Perfect

??

concatenation of an int to a string coerces to a string

Can someone explain why this would work?
didnt they want the answer in string format?

According to the condition of the problem, the length of the array is guaranteed to be > 1, in the examples it can be seen that the first element in the incoming array is "thrown out", this is logical, because checking for i % 0 will not make sense. That's why we start the sequence with 1

Is there any benefit when using a nested ternary operator?

At all, it can be seen that this task can be solved with usage of either time.Duration library or usage of
text.DecimalFormat. Anyway this kata is good for usage of format-method with condition inside.
I am interested now, if the @if@ statment cane be used inside of the format-method.

the array it's the sequence of last digit in fibonacci's numbers. Every 60 numbers the sequence start over

leaky tmp

Okaaay.

RunTime Exception. But the description stays: All inputs are positive, non-zero digits.

What if x or y is equal to 0?

Nice. Learned from it. Thanks

Very clean and simple solution.

impressive implementation of permutations(), very concise and speaks for itself ;)