Hadamard matrices with few distinct types
  The notion of type of quadruples of rows is proven to be useful in the classification of Hadamard matrices. In this paper, we investigate Hadamard matrices with few distinct types. Among other results, the Sylvester Hadamard matrices are shown to be characterized by their spectrum of types. 
A. Mohammadian and B. Tayfeh-Rezaie
math.CO