1. yes 2. yes 3. x x x 0 0 0 x x x 0 0 0 x x x 0 0 0 0 0 0 y y y 0 0 0 y y y 0 0 0 y y y is a 6-by-6 matrix, but just a couple of 3-by-3 matrices x-bloxk and y-block. Not surpising that they multiply independently. So, any multiplication or power property of the smaller blocks is 'cheap' : can be constructed from lower orders (order " in this case). For n=4, 96 matrices have period 12. For n=5, it's 2880. For n=6: 10728. W. -------------------------------------------- dasimov@earthlink.net wrote: Just to be sure I understand: 1. Are you referring to n x n matrices M = (m_ij) with all entries in {-1,0,1} such that i <> j => m_ij + m_ji = 0 ? 2. Do your divisors of 12 (for n = 6) include 12 itself? 3. What exactly is meant by "block matrices along the diagonal" ? Thanks for clarification, Dan