Heaven is Round, Earth is Square

The numbers that yield THE CREATIVE total 216; those which yield THE RECEPTIVE total 144, making in all 360. They correspond with the days of the year.
--Ta Chuan pt. 1, ch. 9, v. 4

"[N]umbers" in this context refers to the yao-numbers, while ䷀ (CREATIVE) and ䷁ (RECEPTIVE) are the first two hexagrams in the traditional sequence.

Two useful representations of the Book of Changes include the square and the cube since both can be used to represent the 64 figures:

64 = 8 x 8
64 = 4 x 4 x 4

Observe the yao-numbers of Receptive and Creative compared with the representations of 64 (above):

144 = 12 x 12
216 = 6 x 6 x 6

In each case we presented two expressions of the form

a. X^2
b. (X/2)^3

144 is a perfect square, 216 is a perfect cube; 64 is both perfect square and cube.