Thus, a = 3q or 3q + 1 or 3q + 2.
Therefore, every number can be represented in three forms.
Case 1: when a = 3q.
a3 = (3q)3 = 27q3 = 9(3q3) = 9m; where m is an integer such that m = 3q3.
Case 2: when a = 3q + 1.
a3 = (3q + 1) 3 = 27q3 + 27q2 + 9q + 1 = 9(3q3 + 3q2 + q) + 1 = 9m + 1; where m is an integer such that m = (3q3 + 3q2 + q).
Case 3: when a = 3q + 2.
a3 = (3q + 2) 3 = 27q3 + 54q2 + 36q + 8 = 9(3q3 + 6q2 + 4q) + 8 = 9m + 8; where m is an integer such that m = (3q3 + 6q2 + 4q).
Hence, cube of any positive integer is of the form 9m, 9m + 1 or 9m + 8.