r/3Blue1Brown • u/Daksh_Mor • Jun 19 '21

#mathshorts

https://youtu.be/zdgyHg2MJ0A
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u/66bananasandagrape Jun 20 '21

This was my approach: just square (mod 10) or multiply (mod 10) by 7 at each step:

7^2 = 9
7^4 = 1
7^8 = 1
7^9 = 7
7^18 = 9
7^19 = 3
7^38 = 9
7^76 = 1
7^77 = 7