Number and quadratic sequences

[Guest]

How do you find the nth term the following number sequences when the second difference is not constant?

729,243,81,27
31250,6250,1250,250

[adamsmith]

Given sequence
1) 729,243,81,27
first sequence we will get by dividing first term by 3
if u divide 729/3=243
243/3=81
81/3=27
there for this is a geometric progression
where r=3,a=729
nth term of GP =ar^(n-1)

2) 31250,6250,1250,250
first sequence we will get by dividing first term by 5
if u divide 31250/6250=5
6250/1250=5
1250/250=5
there for this is a geometric progression
where r=5,a=31250
nth term of GP =ar^(n-1)