Mr. 11 is back to the game!

If x , y , z Z , x,y,z \in \mathbb{Z}, 100 x , y , z 100 -100 \leq x,y,z \leq 100 and x , y , z x,y,z satisfy

x 11 + y 11 = z 11 , x^{11}+y^{11}=z^{11},

then the number of ordered triples ( x , y , z ) (x,y,z) is n n .

If the smallest positive integer k k satisfies the congruence n k 4 ( m o d 11 ) , n\cdot k \equiv 4 \pmod{11}, what is the value of n + k n+k ?

This problem is a part of 11≡ awesome (mod remainders) .


The answer is 611.

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2 solutions

Aditya Raut
Dec 31, 2014

By Fermat's last theorem, x 11 + y 11 = z 11 x^{11} +y^{11}=z^{11} has no non-zero integer solutions.

Hence we conclude that at least one out of x , y , z x,y,z is zero.

Thus the triples ( x , y , z ) (x,y,z) will be of just of 4 types, for m 0 m\neq 0

1. ( m , 0 , m ) 2. ( 0 , m , m ) 3. ( m , m , 0 ) 4. ( 0 , 0 , 0 ) 1. (m,0,m)\\ 2. (0,m,m) \\ 3. (m,-m,0) \\4. (0,0,0)


In the first three cases, k k has 200 200 choices (-100 to 100 excluding zero), giving 200 × 3 = 600 200\times 3 = 600 ordered triples. 4th case will contribute 1 1 triple ,hence n = 601 n=601


We see that 601 7 4 ( m o d 11 ) 601 \equiv 7 \equiv -4 \pmod{11} ,

Hence k 1 ( m o d 11 ) k \equiv -1 \pmod{11} (Because then 601 × k ( 4 ) ( 1 ) 4 ( m o d 11 ) 601\times k \equiv (-4)(-1) \equiv 4 \pmod{11} )

Minimum positive integer value of k k is 10 10 .

Answer n + k = 601 + 10 = 611 n+k = 601+10 =\boxed{611}

Mehul Bafna
Jan 10, 2015

By Fermat's last theorem, the equation has no non-zero integer solutions then we will check for 1)x=0 2)y=0 3)z=0 4)and one case in which three of them simoultaneously equal to zero

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