A178464 - OEIS

%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