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A001231
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Number of nonisomorphic projective planes of order n.
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2
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OFFSET
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2,8
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COMMENTS
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The Bruck-Ryser theorem says that a(n)=0 if n == 1 or 2 (mod 4) and is not the sum of two squares.
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REFERENCES
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CRC Handbook of Combinatorial Designs, 1996, p. 695.
Handbook of Combinatorics, North-Holland '95, p. 672.
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LINKS
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CROSSREFS
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KEYWORD
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nonn,hard,more,nice
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AUTHOR
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STATUS
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approved
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