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%I A294151 #9 Dec 13 2023 04:03:52
%S A294151 1,1,2,3,8,13,36,76,202,482,1281,3277,8749,23083,62056,166498,450576,
%T A294151 1220542,3321870,9057388,24769906
%N A294151 Number of perforated polyominoes with n cells, identifying mirror images.
%C A294151 A perforated polyomino is a polyomino in which every cell has at least one even coordinate.
%e A294151 a(4)=3 because there are 5 tetrominoes, and the skew and square tetrominoes do not lie in the perforated grid, which leaves 3.
%Y A294151 Cf. A000105, number of polyominoes with n cells; A292065, number of Besźel Polycubes with n cells, distinguishing mirror images; A292157, same but identifying mirror images.
%K A294151 nonn,more,hard
%O A294151 1,3
%A A294151 _George Sicherman_, Oct 23 2017
%E A294151 a(16) - a(21) from _Joerg Arndt_, Dec 11 2023

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