I remember reading this problem in some contest, but I don't remember where. I think the contest was 2016 or so. I searched on a few websites with no luck. Do you happen to know what contest it was?
The problem is: Given integers a1, ..., an, We define x0 = 1 and for every 
. Find xn. The solution was O(n * polylog(n)) with FFT.
Topcoder forums don't have a 2B subforum yet, so discuss here.
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