Kata

0, 0, 1, 0, 2, 0, 2, 2, 1, 6, 0, 5, 0, 2, 6, 5, 4, 0, 5, 3, 0, 3, …

This is the Van Eck's Sequence.

Let's go through it step by step.

Term 1: The first term is 0.
Term 2: Since we haven’t seen 0 before, the second term is 0.
Term 3: Since we have seen a 0 before, one step back, the third term is 1
Term 4: Since we haven’t seen a 1 before, the fourth term is 0
Term 5: Since we have seen a 0 before, two steps back, the fifth term is 2.

And so on...

In case you missed it, the rule here is that term n+1 is the "distance" (n - m) between term n, and the highest term m with the same value, where m < n. If there is no such m (ie. We haven't "seen" it before) then the term is 0. For example:

         -------
         V     |  We "saw" a 0 two positions earlier, so the next term is 2
0, 0, 1, 0, 2, 0, ?

Your task is to find the n_th number in Van Eck's Sequence. (1-based)

There are 200 random tests of range 100 to 1000.

Good luck!