let be a positive number 'k' positive integer then let be the power series
$$ f(x)= \sum_{n=0}^{\infty} \frac{(-x)^{n}}{(n!)^k} $$
if $k=0 $ we have $ (1+x)^{-1} $
if $k=1$ we have $ \exp(-x) $
if $k=2$ we have the Bessel function $ J_{0} (2\sqrt{x}) $
but what happens for $ k \ge 3 $