Answer: ar·ith·met·ic pro·gres·sion
/ˌeriTHˌmedik prəˈɡreSH(ə)n/
noun
a sequence of numbers in which each differs from the preceding by a constant quantity (e.g., 3, 6, 9, 12, etc.; 9, 7, 5, 3, etc.).
the relationship between numbers in an arithmetic progression.
"the numbers are in arithmetic progression"
Explanation: