Let A=2^n+3^n+7^n
For a given positive integer n what is the last digit of A?

There may be a more compact way to state this but due to the repeating nature of the last digits of the powers of 2, 3, & 7,

the last digit of the sum is

8 for n mod4=3 or 0
2 for n mod4=1 or 2

Posted by Kenny M on 2011-01-17 16:01:52