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%I #7 Mar 30 2012 16:51:57
%S 1,3,7,11,18,25,34,43,55,67,82,97
%N Minimal number of lines that must be removed from an n X n square array of cells in order to break all rectangles.
%C See Gardner for precise definition.
%D M. Gardner, Mathematical Carnival, Random House, NY, 1975; page 120.
%e To illustrate a(2) = 3: remove edges A, B and C:
%e --A----
%e | | |
%e -----B-
%e | C |
%e -------
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Dec 23 2010
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