This is just an arithmetic sequence because each term is a constant difference from the preceding term, called the common difference.
Any arithmetic sequence can be expressed as:
a(n)=a+d(n-1) where a=initial term, d=common difference, n=term number
In this case a=-8 and d=3 so
a(n)=-8+3(n-1) which you can simplify if you'd like
a(n)=-8+3n-3
a(n)=3n-11
