Find the number of distinct ordered triples that satisfy the equation
,
where are positive (not necessarily distinct) integers.
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A quick overview of one possible method ....
Let x = a + 2 , y = b + 2 and z = c + 2 . Then the given equation becomes
x 1 + y 1 + z 1 = 2 1 .
Now look for solutions with 3 ≤ x ≤ 6 and x ≤ y ≤ z . A straightforward search gives us the following triples ( x , y , z ) :
( 3 , 7 , 4 2 ) , ( 3 , 8 , 2 4 ) , ( 3 , 9 , 1 8 ) , ( 3 , 1 0 , 1 5 ) , ( 3 , 1 2 , 1 2 ) , ( 4 , 5 , 2 0 ) , ( 4 , 6 , 1 2 ) , ( 4 , 8 , 8 ) , ( 5 , 5 , 1 0 ) and ( 6 , 6 , 6 ) .
This translates to the following triples ( a , b , c ) :
( 1 , 5 , 4 0 ) , ( 1 , 6 , 2 2 ) , ( 1 , 7 , 1 6 ) , ( 1 , 8 , 1 3 ) , ( 1 , 1 0 , 1 0 ) , ( 2 , 3 , 1 8 ) , ( 2 , 4 , 1 0 ) , ( 2 , 6 , 6 ) , ( 3 , 3 , 8 ) and ( 4 , 4 , 4 ) .
Factoring in all distinct permutations of these 1 0 triples gives us a final number of 4 6 ordered triples satisfying the original equation.