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A054515
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Number of ways to place non-intersecting diagonals in convex (n+2)-gon so as to create no quadrilaterals.
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1
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1, 2, 6, 21, 78, 301, 1198, 4888, 20340, 85986, 368239, 1594183, 6965380, 30675399, 136026759, 606848034, 2721783023, 12265670909, 55511013680, 252193872912, 1149742659556, 5258257323304, 24117924005616
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OFFSET
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1,2
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LINKS
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Table of n, a(n) for n=1..23.
L. Smiley, Generalization and some variants
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EXAMPLE
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a(3)=6 because the pentagon allows null placement and five ways to place two diagonals.
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MATHEMATICA
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InverseSeries[Series[(y-2*y^2+y^3-y^4)/(1-y), {y, 0, 24}], x] (* then A(x)=[y(x)-x]/x *)
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CROSSREFS
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A046736, A049124, A003168, A054514.
Sequence in context: A124292 A129776 A129775 * A216490 A150190 A150191
Adjacent sequences: A054512 A054513 A054514 * A054516 A054517 A054518
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KEYWORD
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nonn
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AUTHOR
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Len Smiley (smiley(AT)math.uaa.alaska.edu), Apr 08 2000
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STATUS
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approved
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