number of functional dependencies

number of functional dependencies

Find the number of functional dependencies in a relation having n attributes?
On first thought , I figure out that left hand side can have N+1
possibilities(null can also be there.) and similarly N+1 possibility for
right hand side.
Hence total no of FD should be
(n+1)*(n+1) - 1
But ans given is 2^(n+1) .
On analyzing the answer , We can see they are not including trivital ones
like ABC -> A etc .
So what should be the correct ans ???