good question.

prove that the tens digit of every power integral power of 3 is an even number.
like 3^5 = 243. here it is 4.

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21
Shubhodip ·

3^l\equiv 3,9,7,1 \pmod {10} when l\equiv 1,2,3,0 \pmod{4} respectively. Easy to check that 3^l\equiv 3,9,7,1\pmod{20} when l\equiv 1,2,3,0 \pmod{4} respectively. So the claim is true...

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