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A128650
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Number of polygons on n vertices with exactly three faces.
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4
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0, 4, 16, 60, 224, 840, 3168, 12012, 45760, 175032, 671840, 2586584, 9984576, 38630800, 149768640, 581690700, 2262890880, 8815845720, 34389986400, 134312002440, 525129633600, 2055166429680, 8050465600320, 31561484455800
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OFFSET
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2,2
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LINKS
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FORMULA
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a(n) = 4*(n-2)/(n-1) * C(2*n-4,n-2).
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MATHEMATICA
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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