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A001843
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The coding-theoretic function A(n,4,4).
(Formerly M2644 N1052)
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2
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1, 1, 3, 7, 14, 18, 30, 35, 51, 65, 91, 105, 140, 157, 198, 228, 285, 315, 385
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OFFSET
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4,3
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COMMENTS
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Maximal number of 4-subsets of an n-set such that any two subsets meet in at most 2 points.
The initial known values are 1, 1, 3, 7, 14, 18, 30, 35, 51, 65, 91, 105, 140, 157, 198, 228, 285, 315, 385, 418 or 419, 498, 550, 650, 702, 819, 877, 1005, 1085, 1240, 1320, 1496, >= 1576, ...
The first two open cases are A(23,4,4) >= 418 and A(35,4,4) >= 1576.
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REFERENCES
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CRC Handbook of Combinatorial Designs, 1996, p. 411.
R. K. Guy, A problem of Zarankiewicz, in P. Erdős and G. Katona, editors, Theory of Graphs (Proceedings of the Colloquium, Tihany, Hungary), Academic Press, NY, 1968, pp. 119-150.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Table of n, a(n) for n=4..22.
A. E. Brouwer, Bounds for constant weight binary codes
A. E. Brouwer, J. B. Shearer, N. J. A. Sloane and W. D. Smith, New table of constant weight codes, IEEE Trans. Info. Theory 36 (1990), 1334-1380.
R. K. Guy, A problem of Zarankiewicz, Research Paper No. 12, Dept. of Math., Univ. Calgary, Jan. 1967. [Annotated and scanned copy, with permission]
L. Ji, Asymptotic Determination of the Last Packing Number of Quadruples, Designs, Codes and Cryptography 38 (2006) 83-95.
Index entries for sequences related to A(n,d,w)
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FORMULA
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Known exactly for all n except n == 11 mod 12 - see Theorem 5 of Brouwer et al. and Ji.
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EXAMPLE
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For n=7 use all seven cyclic shifts of 1110100.
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CROSSREFS
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Sequence in context: A310268 A190700 A267448 * A310269 A033808 A310270
Adjacent sequences: A001840 A001841 A001842 * A001844 A001845 A001846
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KEYWORD
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nonn,hard,nice,more
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AUTHOR
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N. J. A. Sloane
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EXTENSIONS
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Revised by N. J. A. Sloane and Andries E. Brouwer, May 08 2010
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STATUS
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approved
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