What are the difference numbers of the following arithmetic number sequences?

a) [[$ 1, 3, 5, 7, … $]]

Answer: The difference number of the arithmetic number sequence is .

b) [[$ 20, 15, 10, 5 … $]]

Answer: The difference number of the arithmetic number sequence is .

c) [[$ -1, -2, -3, -4, -5, … $]]

Answer: The difference number of the arithmetic number sequence is .