This is smaller problem of a bigger question.
Example:
if $N= 3$,
then answer is $5$ as groups would be $\{(1),(2),(3)\},\{(1),(2,3)\},\{(1,2),(3)\},\{(1,3),(2)\},\{(1,2,3)\}$
Problem I am facing $\to$ To make a generalized formula for this?
with $n=1$ it is $1$, i.e. $\{(1)\}$
with $n=2$ it is $2$ i.e. $\{(1),(2)\},\{(1,2)\}$, i.e. $2$ can either be clubbed with $1$ or taken separately in $\{(1)\}$
with $n=3$, it is $5$, i.e. $3$ can either be clubbed with $1$ or with $2$ or taken separately in its first grouping in $n=2$ taken separately or with $(1,2)$ in its second grouping
with $n=4$, it is $15$. I cannot make out generalized formula for this.