/tmp/dfs T(n,k)=Number of idempotent nXn 0..k matrices of rank n-1 Rows n=1..6 match a(k) = 1 a(k) = 4*k + 2 a(k) = 6*k^2 + 12*k + 3 a(k) = 8*k^3 + 24*k^2 + 24*k + 4 a(k) = 10*k^4 + 40*k^3 + 60*k^2 + 40*k + 5 a(k) = 12*k^5 + 60*k^4 + 120*k^3 + 120*k^2 + 60*k + 6 (rank n-1 = trace n-1) rhhardin at mindspring.com rhhardin at att.net (either)