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 A272070 Number of ways to quarter a 2n+1 X 2n+1 chessboard with central square removed. 1
 1, 7, 104, 3970, 431932, 137066448, 128095791922, 355704307903818, 2952926822418475378, 73569487283165427567144, 5515501712040561162370942752, 1246743475892797935712690352483842, 850999652841310762943520023896881419780 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The chessboard must be dissected into four identical pieces. All solutions have 90 degree rotational symmetry and solutions that differ only by rotation or reflection are considered equivalent. LINKS FORMULA a(n) = A006067(2*n+1). MATHEMATICA A006067 = Import["https://oeis.org/A006067/b006067.txt", "Table"][[All, 2]]; a[n_] := A006067[[2n+1]]; a /@ Range[1, 13] (* Jean-François Alcover, Sep 14 2019 *) CROSSREFS Cf. A006067, A064941, A257952. Sequence in context: A224706 A001921 A215552 * A098362 A093741 A139742 Adjacent sequences:  A272067 A272068 A272069 * A272071 A272072 A272073 KEYWORD nonn AUTHOR Andrew Howroyd, Apr 19 2016 STATUS approved

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Last modified January 19 20:41 EST 2020. Contains 331066 sequences. (Running on oeis4.)