© CAMBRIDGE UNIVERSITY PRESS 1999

2.3. Number Density of Clusters

The number density of clusters is a strong function of cluster richness. Integrated cluster densities, n_c (> N_R), representing the number density of clusters above a given richness threshold, and the associated mean cluster separation, d ( n_c^-1/3), are listed in Table 3 (Bahcall and Cen 1993).

Table 3. Number Density of Clusters.

R	NR	nc (> NR)h3 (Mpc-3) a	d (> NR) h-1 (Mpc)
0	30	13.5 × 10-6	42
1	50	6.0 × 10-6	55
2	80	1.2 × 10-6	94
3	130	1.5 × 10-7	188
a Approximate uncertainties are 10± 0.2 for the R 0,1,2 densities and 10± 0.3 for R 3.