Present or Past

For every positive integer n n , the number 310 0 n 65 0 n 55 8 n + 11 7 n 3100^n - 650^n - 558^n + 117^n is divisible by :

2013 2009 2015 2011

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2 solutions

Curtis Clement
Feb 28, 2015

testing n= 1 gives an answer of 2009. Now I shall prove that the expression is divisible by 2009 for all n by using modular arithmetic, as follows... 2009 = 7 2 × 41 2009 = 7^2 \times \ 41 310 0 n 65 0 n 55 8 n + 11 7 n 6 n 6 n 5 n + 5 n 0 m o d ( 7 ) \rightarrow\ 3100^n - 650^n -558^n +117^n \equiv 6^n - 6^n -5^n +5^n \equiv 0 mod(7) 310 0 n 65 0 n 55 8 n + 11 7 n 2 5 n 3 5 n 2 5 n + 3 5 n 0 m o d ( 41 ) \rightarrow\ 3100^n - 650^n -558^n +117^n \equiv 25^n - 35^n - 25^n +35^n \equiv 0 mod(41) 2009 ( 310 0 n 65 0 n 55 8 n + 11 7 n ) a s r e q u i r e d \therefore\ 2009| (3100^n - 650^n -558^n +117^n) \ as \ required

Fox To-ong
Jan 13, 2015

based from the choices, the least value possible is 2...

please post some detailed and novel solutions ...

Ganesh Ayyappan - 6 years, 5 months ago

1 works too.

Omkar Kulkarni - 6 years, 4 months ago

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