Count good sets with given conditions We need to find the numbers of good sets in a sequence. The good set is:
A good set is a sequence of $P$ positive integers which satisfies the following 2 condition :


*

*If an integer $L$ appears in a sequence then $L-1$ should also appear in the sequence

*The first occurrence of $L-1$ comes before the last occurrence of $L$


Example : Let $P=3$ then answer is $6$
Explanation : The total number of output sets are $6$
One of the solution set is: 
[1,1,1], [1,1,2], [1,2,1], [1,2,2], [2,1,2], [1,2,3]

For [$1,2,3$]= The first occurrence of $1$ comes before the last occurrence of $2$ and the last occurrence of $3$.

When P=1, there is 1 good set.
[1]

When P=2, there are 2 good sets.
[1,1] and [1,2]

When P=3, there are 6 good sets.
[1,1,1], [1,1,2], [1,2,1], [1,2,2], [2,1,2], [1,2,3]

This pattern looks like it might be P!
Check if there are 4! = 24 sets for P = 4.
[1,1,1,1] ... [1,2,3,4]
