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%I #38 Mar 22 2024 18:49:15
%S 0,1,1,4,5,9,12,17,21,27,33,41,48,56,65,75,85,96,108,121,133,146,161,
%T 176,190,208
%N Heyawake numbers: maximum number of painted cells in an n X n grid, such that no two painted cells are orthogonally adjacent and the unpainted cells form a contiguous area.
%C Inspired by the Japanese puzzle of the same name.
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Heyawake">Heyawake</a>.
%F a(n) = A239072(n-4) + 2*n - 2 for n > 4.
%e If n=6, the painted cells could be A1, A3, A6, B5, C1, C3, D4, D6, E2, F1, F4, F6 (12 cells in all).
%Y Cf. A239072 (makes up the inner n-4 X n-4 square of the grid).
%K nonn,more
%O 0,4
%A _Elliott Line_, Mar 13 2014
%E Some values corrected, incorrect values removed by _Elliott Line_, Aug 21 2014
%E a(16) and a(20) corrected by _Elliott Line_ at the suggestion of Greg Malen, Sep 02 2020
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