Where can I find the construction for a **skew Hadamard matrix** of order 756?


According to multiple papers (e.g. [Koukouvinos and Stylianou - On skew-Hadamard matrices](https://www.sciencedirect.com/science/article/pii/S0012365X07004013?via%3Dihub) and [Seberry - On skew Hadamard matrices](https://ro.uow.edu.au/cgi/viewcontent.cgi?article=2003&context=infopapers)) this matrix has been constructed. However, none of the papers I have found give a reference to the actual construction that is being used to obtain it. In particular, the paper by Seberry (published in 1978) is the oldest I could find which states that the construction is known.


Note that I also couldn't find a construction for a skew Hadamard matrix of order 292 (see [this question](https://mathoverflow.net/questions/439195/construction-of-skew-hadamard-matrix-of-order-292)), which also appeared as known for the first time in that same 1978 paper, so it is possible that they were created using the same construction.



How to construct a skew Hadamard matrix of order 756?
The matrix can be constructed using Theorem 7 from [Seberry - On skew Hadamard matrices](https://ro.uow.edu.au/cgi/viewcontent.cgi?referer=&httpsredir=1&article=2003&context=infopapers), by setting $m = 1$ and $n = 28$.


The amicable Orthogonal Design of type $((1, 27); (28))$ are constructed from amicable hadamard matrices of order 28 (construction taken from [(v, k, λ) Configurations and Hadamard matrices - Wallis](https://www.cambridge.org/core/journals/journal-of-the-australian-mathematical-society/article/v-k-configurations-and-hadamard-matrices/DB40CEDE6B57B928253CF7A47750FEF4), for the relation between amicable Hadamard matrices and amicable OD see Lemma 5.4 from [Orthogonal Designs - Seberry](https://link.springer.com/book/10.1007/978-3-319-59032-5)).


Lastly, the OD of type $(1, 1, 26)$ is constructed using the Goethals-Seidel Array and sequences taken from Table G.7 of [Orthogonal Designs - Seberry](https://link.springer.com/book/10.1007/978-3-319-59032-5)


