31. If a positive integer can be expressed as the difference of cubes of two consecutive odd numbers, it is called a "harmonious number". For example: $2=1^{3}-(-1)^{3}, 26=3^{3}-1^{3}, 2$ and 26 are both "harmonious numbers". Then, among the positive integers not exceeding 2021, the sum of all "harmonious numbers" is . $\qquad$
Answer: 6860