\[=1+\cfrac{z}{1-(z/2)+\cfrac{z^{2}/(4\cdot 3)}{1+\cfrac{z^{2}/(4\cdot 15)}{1+%
\cfrac{z^{2}/(4\cdot 35)}{1+}}}}\cdots\cfrac{z^{2}/(4(4n^{2}-1))}{1+}\cdots\]