Well the rule for any geometric sequence is:
a(n)=ar^(n-1), a=initial term, r=common ratio, n=term number.
Here we have a common ratio of:
4/16=1/4=(1/4)/1=r=1/4 and an initial value of 16 so the formula becomes:
a(n)=16(1/4)^(n-1) so the sixth term would be:
a(6)=16(1/4)^5
a(6)=16/1024
a(6)=1/64
