Math Help - Generating Functions

1. Generating Functions

Find the generating functions for the following sequences, express them in a closed form, without infinite sums:

(i) 1,2,1,4,1,8,1,16,1,...

(ii)1,1,0,1,1,0,1,1,0,...

This is what I have so far:
(i)i've written it as 1 + 2^1*x^1 + (2x)^0 + 2^2*x^3 + (2x)^0 + 2^3*x^5 +...
if the sequence didnt have all the ones inbetween, I think i'd know how to do it, using differentiation on (1/(1-x)) multiplied by something. But I'm not sure how to incorporate the ones into the sequence...

2. Originally Posted by pseudonym

Find the generating functions for the following sequences, express them in a closed form, without infinite sums:

(i) 1,2,1,4,1,8,1,16,1,...

(ii)1,1,0,1,1,0,1,1,0,...

This is what I have so far:
(i)i've written it as 1 + 2^1*x^1 + (2x)^0 + 2^2*x^3 + (2x)^0 + 2^3*x^5 +...
if the sequence didnt have all the ones inbetween, I think i'd know how to do it, using differentiation on (1/(1-x)) multiplied by something. But I'm not sure how to incorporate the ones into the sequence...

The generating function for (i) has the form $1 + 2x + x^2 + 4x^3 + x^4 \cdots$. It is the same thing with $(1 + x^2 + x^4 +....) + 2x(1 + 2x^2 + 4x^4 \cdots )$. Now consider the power series of $1/(1-x^2)$ and $1/(1-2x^2)$.
The second problem is similar. The generating function for (ii) has the form $1+x+x^3+x^4+x^6...= (1+x^3+x^6 \cdots)+x(1+x^3+x^6 \cdots)$. Now consider the power series of $1/(1-x^3)$.