Hello,
Your sequence is arithmetic.
10.5-9=1.5
9-7.5=1.5
7.5-6=1.5
6-4.5=3
4.5-3=1.5
3-1.5=1.5
1.5-1.5=0
...
f(x)=f(n-1)-1.5 is the iterative rule.
f(1)=10.5
f(2)=10.5-1.5=9
f(3)=10.5-21.5=7.5
f(4)=10.5-31.5=6
...
f(n)=10.5-1.5*(n-1) is the general form.
