The number 12 is exactly divisible by six numbers (i.e. 1, 2, 3, 4, 6, and 12). The number 243 is also exactly divisible by six numbers (i.e. 1, 3, 9, 27, 81 and 243).

There are 16 numbers in the range of 1-100 that are exactly divisible by six numbers (i.e. 12, 18, 20, 28, 32, 44, 45, 50, 52, 63, 68, 75, 76, 92, 98 and 99). How many numbers in the range of 1-20000 are exactly divisible by six numbers?