### How many graphs?

Posted:

**Sun Jan 04, 2009 7:48 pm**How many different graphs are with V vertex?

The graph should be: Directed, connected, with no self-loops and no "parallel-edges" (namely the same start-point and end-point).

I'm trying to solve this problem for a long long time...

I really would appreciate if someone can point me some hint.

PS: The problem was in a online contest, and I wasn't able to find it again.

Thanks in advance, John.

The graph should be: Directed, connected, with no self-loops and no "parallel-edges" (namely the same start-point and end-point).

I'm trying to solve this problem for a long long time...

I really would appreciate if someone can point me some hint.

PS: The problem was in a online contest, and I wasn't able to find it again.

Thanks in advance, John.