Yup, I haven't try to pass that expression directly to Wolfram. Was only trying to check my way of solution, my fault. Now I've found that for some scenarious it leeds to error... Thank you!

If you type those inputs 8132 ^ 21302 into Wolfram:

https://www.wolframalpha.com/input?i=8132+%5E+21302

you can scroll down and see under "Last few decimal digits": ...4122599424.

So since the full number ends in 4, then the remainder mod 5 will be 4 also in this case. So 4 seems correct on Wolfram for the inputs 8132 ^ 21302

edit - here is the direct link for Wolfram language mod operator - https://www.wolframalpha.com/input?i=%288132+%5E+21302%29+mod+5 where the answer is also given as 4 so I don't know where you are reading 0 as the answer given on that site?

Hello! I can't understand why do you put the last one arr[i] in brakets (arr[i] = arr[i+1], arr[i+1] = e, arr[i])? Can you please explain to me this magic?