Shalosh B. Ekhad Doron Zeilberger The Number of Solutions of X^2=0 in Triangular Matrices Over GF(q). 1996 3 Electr. J. Comb. 1 http://www.combinatorics.org/Volume_3/Abstracts/v3i1r2.html db/journals/combinatorics/combinatorics3.html#EkhadZ96