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 A268404 Number of fixed polyominoes that have a width and height of n. 5
 1, 5, 111, 7943, 1890403, 1562052227, 4617328590967, 49605487608825311, 1951842619769780119767, 282220061839181920696642671, 150134849621798165832163223922131, 293909551918134914019004192289440616787, 2116817972794640259940977362779552773322908743 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Iwan Jensen originally provided this sequence. The sequence also describes the water patterns of lakes in the water retention model. A lake is defined as a body of water with dimensions of n X n when the size of the square is (n+2) X (n+2). All other bodies of water are ponds. The 3 X 3 square serves as a tutorial for the following three nomenclatures: 1) The total number of unique water patterns equals 102 and includes lakes and ponds.  2) The number of free lake-type polyominoes equals 24.  3) The number of fixed lake-type polyominoes equals 111.  See the explanatory graphics in the link section. John Mason has looked at free polyominoes in rectangles A268371. Anna Skelt initiated the discussion on the definition of a lake. LINKS Andrew Howroyd, Table of n, a(n) for n = 1..15 Craig Knecht, 4x4 minimal lake area patterns Craig Knecht, 5x5 minimal lake area patterns Craig Knecht, 6x6 minimal lake area patterns Craig Knecht, 7x7 minimal lake area patterns Craig Knecht, 24 free lake-type polyominoes 3x3 Craig Knecht, Polyominoe enumeration Craig Knecht, Walter Trump's 111 fixed lake-type polyominoes 3x3 Wikipedia, Water Retention on Mathematical Surfaces EXAMPLE There are many interesting ways to connect all boundaries of the square with the fewest number of edge-joined cells. 0 0 0 0 1 0 0 0 0 0 1 1 0 0 1 1 1 0 0 0 1 0 0 0 1 1 1 0 0 0 0 1 0 0 0 0 MATHEMATICA A292357 = Cases[Import["https://oeis.org/A292357/b292357.txt", "Table"], {_, _}][[All, 2]]; a[n_] := A292357[[2n^2 - 2n + 1]]; Array[a, 15] (* Jean-François Alcover, Sep 10 2019 *) CROSSREFS Main diagonal of A292357. Cf. A054247 (all unique water retention patterns for an n X n square), A268311 (free polyominoes that connect all boundaries on a square), A268339 (lake patterns that are invariant to all transformations). Sequence in context: A219161 A284461 A002400 * A258795 A263531 A258177 Adjacent sequences:  A268401 A268402 A268403 * A268405 A268406 A268407 KEYWORD nonn AUTHOR Craig Knecht, Feb 03 2016 EXTENSIONS a(12)-a(13) from Andrew Howroyd, Oct 02 2017 STATUS approved

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Last modified December 9 03:42 EST 2021. Contains 349625 sequences. (Running on oeis4.)