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 A001231 Number of nonisomorphic projective planes of order n. 1
 1, 1, 1, 1, 0, 1, 1, 4, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,8 COMMENTS The Bruck-Ryser theorem says that a(n)=0 if n == 1 or 2 (mod 4) and is not the sum of two squares. REFERENCES CRC Handbook of Combinatorial Designs, 1996, p. 695. Handbook of Combinatorics, North-Holland '95, p. 672. LINKS C. W. H. Lam, Publications C. W. H. Lam, The Search for a Finite Projective Plane of Order 10, American Mathematical Monthly, 98, (no. 4) 1991, 305 - 318. C. W. H. Lam, G. Kolesova and S. Swiercz, A computer search for finite projective planes of order 9, Discrete Math., 92 (1991), 187-195. C. W. H. Lam, L. Thiel and S. Swiercz, The non-existence of finite projective planes of order 10, Canad. J. Math., 41 (1989), 1117-1123. G. Eric Moorhouse, Projective Planes of Small Order N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98). Eric Weisstein's World of Mathematics, Projective Planes CROSSREFS Sequence in context: A115527 A050920 * A141150 A089418 A124856 A061858 Adjacent sequences:  A001228 A001229 A001230 * A001232 A001233 A001234 KEYWORD nonn,hard,more,nice AUTHOR STATUS approved

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