The function below shows the number of car owners f(t), in thousands, in a city in different years t:
f(t) = 0.25t2 − 0.5t + 3.5
the average rate of change of f(t) from t = 2 to t = 6 is thousand owners per year

(n^3 - n)

= n(n-1)(n+1)

since it is divisible by 3 and 2 ,because it is a multiple 3 consecutive number

if, n-1 is odd then n+1 is also odd, then it is a multiple of 9

but if, n-1 is even then n+1 is also even, then it is a multiple of 4

so, largest multiple = max(9*2, 4*3) = max(18, 12) = 18