Geodesic
On the existence of (196,91,42) Hadamard difference sets
Kragujevac Journal of Mathematics, Tome 34 (2010), p. 113

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We use group representations and factorization in the cyclotomic rings to show that $(196, 91, 42)$ Hadamard difference sets exist only in group $(C_7 \times C_7)\rtimes C_4$ with Gap location number $[196, 8]$. We also show that $(980,89,8)$ difference sets may only exist in four groups of order $980$.
Classification : 05B10 05B20
Keywords: Representation, Idempotents, Menon-Hadamard difference Sets, Intersection numbers 
Adegoke S. A. Osifodunrin. On the existence of (196,91,42) Hadamard difference sets. Kragujevac Journal of Mathematics, Tome 34 (2010), p. 113 . http://geodesic.mathdoc.fr/item/KJM_2010_34_a9/
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     author = {Adegoke S. A. Osifodunrin},
     title = {On the existence of (196,91,42) {Hadamard} difference sets},
     journal = {Kragujevac Journal of Mathematics},
     pages = {113 },
     year = {2010},
     volume = {34},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/KJM_2010_34_a9/}
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