Here are some approxmiate probabilities for number of people n:
n Prob(no matches) -- ---------- 2 50.000000% 3 33.333333% 4 37.500000% 5 36.666667% 6 36.805556% 7 36.785714% 8 36.788194% 9 36.787919% 10 36.787946% 11 36.787944% 12 36.787944% 13 36.787944% 14 36.787944% 15 36.787944%Note that the probabilities quickly converge to 1/e.
Michael Shackleford, A.S.A.