Find an expression which yields the number of ways to split a 2 by N rectangle into two polyominoes. Rotations and reflections are NOT considered distinct.

For example, if N=1 there is only one way - two 1x1 squares.

If N=2 then there are two ways - one way is a 1x1 square with an "L" shape and two 2x1 rectangles as the other.

If N=3 then there are the 6 ways as depicted:

a a a a a a	a a a a a a	a a a a a a
a a a a a a	a a a a a a	a a a a a a