Saturday, November 23, 2019

elementary number theory - Finding the remainder of a factorial using modular arithmetic

How do I find the remainder of 52001+(27)! when it is divided by 8? Can someone please show me the appropriate steps? I'm having a hard time with modular arithmetic.



So far this is how far I've got:



5^2=25 \equiv 1\pmod{8}



So \begin{align}5^{2001}&=5^{2000}\cdot 5\\ &=(5^2)^{1000}\cdot 5\\ &=25^{1000}\cdot 5\\ &\equiv 1^{1000}\cdot 5\\ &\equiv 5 \pmod{8}\end{align}



How do I go about somthing similar for 27!? Also, could someone direct me to a video or some notes where I can learn this?

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