%I A001843 M2644 N1052
%S A001843 1,1,3,7,14,18,30,35,51,65,91,105,140
%N A001843 The coding-theoretic function A(n,4,4).
%C A001843 Maximal number of 4-subsets of an n-set such that any two subsets meet 
               in at most 2 points.
%D A001843 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A001843 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A001843 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.
%D A001843 CRC Handbook of Combinatorial Designs, 1996, p. 411.
%D A001843 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.
%H A001843 E. M. Rains and N. J. A. Sloane, <a href="http://www.research.att.com/
               ~njas/codes/Andw/">A(n,d,w) tables</a>
%H A001843 <a href="Sindx_Aa.html#Andw">Index entries for sequences related to A(n,
               d,w)</a>
%F A001843 Known exactly for all n except n == 5 mod 6 - see Theorem 5 of Brouwer 
               et al.
%e A001843 For n=7 use all cyclic shifts of 11101000.
%Y A001843 Sequence in context: A128661 A009461 A143630 this_sequence A033808 A161210 
               A154772
%Y A001843 Adjacent sequences: A001840 A001841 A001842 this_sequence A001844 A001845 
               A001846
%K A001843 nonn,hard,nice
%O A001843 4,3
%A A001843 N. J. A. Sloane (njas(AT)research.att.com).
%E A001843 The first unkown value is a(17), known to be >= 156. It would be nice 
               to settle this case!