A number theory problem by vishwathiga jayasankar

Does there exists a positive integer n n such that the last digit of 6 n 6^n is 0?

No Yes

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2 solutions

Anthony Holm
Oct 2, 2016

If the last digit of any number is 0 it must be divisible by 10. Because 6=3*2 and there is no factor of 5, any power of 6 is never divisible by 5 and thus also never by 10 meaning a power of 6 can never end with a digit of 0

Jesse Nieminen
Oct 9, 2016

6 6 2 ( m o d 10 ) 6 n 6 ( m o d 10 ) , n Z + 6 \equiv 6^2 \pmod{10} \implies 6^n \equiv 6 \pmod{10}, \quad n \in \mathbb{Z}_+

Hence, the answer is No \boxed{\text{No}} .

same way that I did it

chase marangu - 3 years, 2 months ago

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