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Hadamard Matrix of Order 668 | Epoch AI Find a Hadamard matrix of order 668. Write your Hadamard matrix to an .npy file (using numpy.save) and output the filepath. The matrix must be a square array of +1 and -1 entries. BibTeX Citation @misc{epoch2026, title={Hadamard Matrix of Order 668}, author={{Epoch AI}}, year={2026}, url={https://epoch.ai/frontiermath/open-problems/hadamard}, note={Accessed: 2026-08-12}} Hadamard Matrix of Order 668 "Hadamard Matrix of Order 668" — a problem from FrontierMath: Open Problems, Epoch AI's benchmark of unsolved research mathematics.