Inspired by Tom's questions and Andrew's calculations, I wrote
a program to place stars randomly on a CCD and calculate the
distance to nearest neighbors. The results are in Tech Note 66:
http://a188-L009.rit.edu/tass/technotes/tn0066.html
The Note shows results for cases from 1,000 to 9,000 stars
scatted over an image.
Michael Richmond