Observation is important

Algebra Level 5

Let A A be a m × m m\times m matrix with all elements equal to 1 such that A n = 1 6 17 A A^n= 16^{17}A , where m m and n n are positive integers. Find the sum of all possible value of n n .


The answer is 132.

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1 solution

Ong Zi Qian
Oct 18, 2017

Given that A n = 1 6 17 A A^n=16^{17}A , so A n 1 = ( 2 4 ) 17 = 2 68 A^{n-1}=(2^4)^{17}=2^{68} .

Therefore, n 1 n-1 is a factor of 68,

the sum of all possible value of n 1 n-1 is the sum of factor of 68 ( = 2 2 × 1 7 1 ) 68(=2^2\times 17^1) ,

so the sum of all possible value of n 1 n-1 is ( 2 0 + 2 1 + 2 2 ) ( 1 7 0 + 1 7 1 ) = 7 × 18 = 126 (2^0+2^1+2^2)(17^0+17^1)=7\times 18=126

Due to there are ( 2 + 1 ) ( 1 + 1 ) (2+1)(1+1) n n , therefore the sum of all possible value of n n is 126 + 6 = 132 126+6=132

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