If I have n dots, how many configurations exist for lines that connect them, including no connections? For example, if I have 0, or 1 dots I believe this should be 0 since no connections are possible (or perhaps I should consider the single dot as having a single connection to itself?) If I have 2 dots, there would be two possibilities, one connection between the two, and zero connections. To clarify what I mean, for three dots I counted 8: http://i.imgur.com/EHZLcYe.png For four dots I counted 65, but I could be wrong as I was drawing them and this is error prone: http://imgur.com/Zw0JM0j The final possibility used 6 lines. I tried looking through various possibilities and renditions in OEIS, but nothing popped out. I'm having trouble coming up with a function that returns such an odd sequence as 0,0,2,8,65. I'm hoping that I goofed, because 0,0,2,8,64 looks a lot more palpable. Surely this function is known? Or something very similar? Thank you for your time.