This is an arithmetic sequence because each terms is a constant difference, called the common difference, from the term preceding it. Any arithmetic sequence can be expressed as:
a(n)=a+d(n-1), a=initial term, d=common difference, n=term number.
d=39-31=31-23=23-15, etc=8, and we can see a=7 so
a(n)=7+8(n-1) which we can simplify
a(n)=8n-1, so the 6th and 7th terms are:
47 and 55
