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A140106
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Number of noncongruent diagonals in a regular n-gon.
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1
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0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 28, 28, 29, 29, 30, 30, 31, 31, 32, 32, 33, 33, 34, 34, 35, 35, 36, 36, 37
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,6
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COMMENTS
| Number of double-stars (diameter 3 trees) with n nodes. For n >= 3, number of partitions of n-2 into two parts. - W. Bomfim, Feb 12 2011
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LINKS
| Index entries for sequences related to trees
W. Bomfim, Double-star corresponding to the partition [3,7]
Index to sequences with linear recurrences with constant coefficients, signature (1,1,-1).
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FORMULA
| For n > 1, floor((n-2)/2), otherwise 0. - W. Bomfim, Feb, 12, 2011
G.f.: x^4/(1-x-x^2+x^3). - Colin Barker, Jan 31 2012
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EXAMPLE
| The square (n=4) has two congruent diagonals; so a(4)=1. The regular pentagon also has congruent diagonals; so a(5)=1. Among all the diagonals in a regular hexagon, there are two noncongruent ones; hence a(6)=2, etc.
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CROSSREFS
| Essentially the same as A004526. [From Joseph Myers (jsm(AT)polyomino.org.uk), Sep 05 2009]
Cf A000554. - W. Bomfim, Feb, 12, 2011
Sequence in context: A130472 A076938 A004526 * A123108 A008619 A110654
Adjacent sequences: A140103 A140104 A140105 * A140107 A140108 A140109
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KEYWORD
| nonn,easy
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AUTHOR
| Andrew McFarland (andrewmcfarland1(AT)hotmail.com), Jun 03 2008
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EXTENSIONS
| More terms from Joseph Myers (jsm(AT)polyomino.org.uk), Sep 05 2009
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![Double-star corresponding to the partition [3,7]](http://oeis.org/wiki/File:Ff2.png){kind=link}