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Explanation:
When we divide 2021 over 337, then we get 5 remainder 336. That remainder 336 is the same as remainder -1, since we're one away from landing on 337. We're one short of that goal.
The remainder -1 allows us to quickly compute the remainder of 2021^x, where x is any positive whole number. If x is odd, then 2021^x will lead to a remainder of -1. If x is even, then 2021^x over 337 leads to a remainder of 1. This is because something like (-1)^2 = 1. So any even power results in a positive value.
