According to the given sample, a_n (the nth term of the sequence) is (2/9) for odd n, beginning with n=1 and continuing: 1, 3, 5, 7, and the next term is always 0. How would you characterize 1, 3, 5, 7, ... ? These are all odd numbers. How would you characterize 2, 4, 6, 8, ... ? These are all even #s.
One way to summarize this behavior is to write the formula
a_n = (2/9) for odd n and 0 for even n.
There are other ways in which you could write such a formula.
