A Combinatorial Object

Hadamard matrix of order 428

F26A Graph

Description: A Hadamard matrix is a square matrix whose entries are either +1 (white pixels) or -1 (black pixels) and whose rows are mutually orthogonal. A Hadamard matrix of order 428, the smallest unknown order of Hadamard matrices before June 2004, was built by Hadi Kharaghani and Behruz Tayfeh-Rezaie. Since June 2004, the order 668 has been the smallest multiple of 4 for which no Hadamard matrix is yet known. It is conjectured that examples of order 4n exist for all n.

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