as stated in this FAQ:
Q: How many people go on an adventure?
Group adventures will be given to groups between 4 and 6 in size. However, no allowances are made for group size, so you should always have 6 if possible.
My understanding is that any group between 3 and 6 can enter and that the instance generated is scaled to both the party size and the average level.
Which is correct?
I've been meaning to try a LDoN, really I have.
____________________________Samatman 70 Shadowknight - Innoruuk
Samatman 85 Death Knight - Silver Hand
Samatman 19 Rogue / 14 Scholar - Runnyeye
Samatman 10 Champion - Brandywine (LoTR beta)
Samatman 7 Wrathguard - Dorzhan