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Search: id:A001843
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| A001843 |
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The coding-theoretic function A(n,4,4).
(Formerly M2644 N1052)
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+0
2
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| 1, 1, 3, 7, 14, 18, 30, 35, 51, 65, 91, 105, 140
(list; graph; listen)
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OFFSET
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4,3
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COMMENT
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Maximal number of 4-subsets of an n-set such that any two subsets meet in at most 2 points.
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REFERENCES
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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.
CRC Handbook of Combinatorial Designs, 1996, p. 411.
R. K. Guy, A problem of Zarankiewicz, in P. Erd\"{o}s and G. Katona, editors, Theory of Graphs (Proceedings of the Colloquium, Tihany, Hungary), Academic Press, NY, 1968, pp. 119-150.
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LINKS
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E. M. Rains and N. J. A. Sloane, A(n,d,w) tables
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 == 5 mod 6 - see Theorem 5 of Brouwer et al.
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EXAMPLE
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For n=7 use all cyclic shifts of 11101000.
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CROSSREFS
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Sequence in context: A058027 A128661 A009461 this_sequence A033808 A115285 A004232
Adjacent sequences: A001840 A001841 A001842 this_sequence A001844 A001845 A001846
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KEYWORD
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nonn,hard,nice
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AUTHOR
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njas
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EXTENSIONS
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The first unkown value is a(17), known to be >= 156. It would be nice to settle this case!
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