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A162674
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Number of different fixed (possibly) disconnected tetrominoes bounded (not necessarily tightly) by an n X n square.
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5
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0, 1, 97, 956, 4780, 16745, 46921, 112672, 241536, 474585, 870265, 1508716, 2496572, 3972241, 6111665, 9134560, 13311136, 18969297, 26502321, 36377020, 49142380, 65438681, 86007097, 111699776, 143490400, 182485225, 229934601
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OFFSET
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1,3
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COMMENTS
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Fixed quasi-tetrominoes.
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LINKS
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FORMULA
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a(n) = n*(n-1)*(8*n^4-16*n^3-9*n^2+17*n+8)/12.
G.f.: x^2*(1+90*x+298*x^2+90*x^3+x^4)/(1-x)^7. [Colin Barker, Apr 25 2012]
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EXAMPLE
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a(2)=1: the (connected) square tetromino.
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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