Calculate the sum $\sum_{n=0}^\infty\frac{1}{(4n)!}$ How to determine the sum $\sum_{n=0}^\infty\frac{1}{(4n)!}$ ?
Do I need to somehow convert (4n)! to (2n)! or in tasks like this, should I get the (4n)! after some multiplying?
Thank you all for your time!

$cos(x) = \sum_{n=0}^\infty(-1)^n\frac{x^{2n}}{(2n)!}$
$cosh(x) = \frac{1}{2}\sum_{n=0}^\infty\frac{x^{n}}{n!} + \frac{1}{2}\sum_{n=0}^\infty(-1)^n\frac{x^{n}}{n!}$
How to get (4n)! from these (2n)! and n!  ?
