Divide 2021 by 19:
2021/19 = 106.3684 = 106 * 19 + 7
Now calculate the remainder of 7^2021
7^1 = 7
7^2 = 49 = 2*19 + 11
7^3 = 343 = 18*19 + 1
7^4 = 2394* 19 + 7
The pattern repeats 7, 11 , 1
So for every time the exponent is increased by 10, the remainder is is the same. ( so a starting value of 1 would have a remainder of 7.
This means the remainder of 2021^2021/19 would be 7
