19^24 mod 21 using Modulo

Solution:
`19^24" mod "21`

Here `19^24=(19^2)^12`

`=(19^2" mod "21)^12" mod "21`

`=(361" mod "21)^12" mod "21`

`=4^12" mod "21`

Here `4^12=(4^3)^4`

`=(4^3" mod "21)^4" mod "21`

`=(64" mod "21)^4" mod "21`

`=1^4" mod "21`

`=1" mod "21`

`=1`

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