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Search: id:A014626
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| A014626 |
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Number of intersection points of diagonals of n-gon, plus number of vertices. |
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+0
2
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| 0, 1, 2, 3, 5, 10, 21, 42, 78, 135, 220, 341, 507, 728, 1015, 1380, 1836, 2397, 3078, 3895, 4865, 6006, 7337, 8878, 10650, 12675, 14976, 17577, 20503, 23780, 27435, 31496, 35992, 40953, 46410, 52395, 58941, 66082, 73853, 82290, 91430, 101311
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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If Y is a 3-subset of an n-set X then, for n>=4, a(n-3) is the number of 4-subsets of X which have neither one element nor two elements in common with Y. Y is a 3-subset of an n-set X then, for n>=4, a(n-3) is the number of (n-4)-subsets of X which have neither one element nor two elements in common with Y.lso, if - Milan R. Janjic (agnus(AT)blic.net), Dec 28 2007
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FORMULA
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(n^4-6*n^3+11*n^2-6*n)/24 +n.
Binomial transform of (0, 1, 0, 0, 1, 0, 0, 0...), or g.f. x+x^4. G.f. : x(1-3x+3x^2)/(1-x)^5; a(n)=C(n, 1)+C(n, 4). - Paul Barry (pbarry(AT)wit.ie), Sep 23 2004
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CROSSREFS
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Sequence in context: A076834 A023170 A125312 this_sequence A132418 A024494 A131708
Adjacent sequences: A014623 A014624 A014625 this_sequence A014627 A014628 A014629
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KEYWORD
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nonn,easy
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AUTHOR
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Mohammad K. Azarian (ma3(AT)evansville.edu)
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EXTENSIONS
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Corrected and extended by Erich Friedman (erich.friedman(AT)stetson.edu).
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