No it is not. All geometric sequences have a common ratio that is a constant found when you divide any term by the previous one.
3/5 !=1/3
So it is not a geometric sequence.
It IS an arithmetic sequence though, as all arithmetic sequences have a common difference that is a constant found when you find the difference between any term and the term preceding it.
3-5=1-3=-1-1=d=2
So there is a common difference of 2 so this is an arithmetic sequence. And all arithmetic sequences can be expressed as:
a(n)=a+d(n-1), a(n)=nth term, a=initial term, d=common difference, n=term number, in this case a=5 and d=-2 so
a(n)=5-2(n-1) which of course can be simplified...
a(n)=5-2n+2
a(n)=7-2n