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A056780
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Rectangular free polyominoes: number of n-celled polyominoes when the cell is a rectangle.
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7
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1, 2, 3, 9, 21, 68, 208, 730, 2542, 9287, 34053, 127112, 476849, 1803636, 6851960, 26157362, 100211446, 385239872, 1485232325, 5741327939, 22246061118, 86383655207, 336093789246, 1309999171971, 5114453234510, 19998176771431, 78306018629550, 307022197845116
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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LINKS
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FORMULA
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MATHEMATICA
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A[s_] := With[{s6 = StringPadLeft[ToString[s], 6, "0"]}, Cases[Import[ "https://oeis.org/A" <> s6 <> "/b" <> s6 <> ".txt", "Table"], {_, _} ][[All, 2]]];
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CROSSREFS
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KEYWORD
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nice,nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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