Those 5 factors on the left average to the middle one n-2, 
so the left side isn't far from 

So the solution to

 

should be close to the correct answer,







So we try 8






n = 8
---------------------

These 3 factors on the left average to the middle one n-1, 
so the left side isn't far from 

So the solution to

 

should be close to the correct answer,







So we try 7






n = 7

Edwin