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Search: id:A051923
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| 1, 9, 42, 140, 378, 882, 1848, 3564, 6435, 11011, 18018, 28392, 43316, 64260, 93024, 131784, 183141, 250173, 336490, 446292, 584430, 756470, 968760, 1228500, 1543815, 1923831
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OFFSET
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0,2
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COMMENT
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If Y is a 3-subset of an n-set X then, for n>=8, a(n-8) is the number of 8-subsets of X having at least two elements in common with Y. - Milan R. Janjic (agnus(AT)blic.net), Nov 23 2007
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REFERENCES
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A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pp. 194-196.
Herbert John Ryser, Combinatorial Mathematics, "The Carus Mathematical Monographs", No. 14, John Wiley and Sons, 1963, pps. 1-8.
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FORMULA
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a(n)=C(n+5, 5)*(n+2)/2.
G.f.: (1+2*x)/(1-x)^7.
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MAPLE
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a:=n->(sum((numbcomp(n, 6)), j=5..n))/2:seq(a(n), n=6..31); [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Aug 26 2008]
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CROSSREFS
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Cf. A051836.
Cf. A093560 ((3, 1) Pascal, column m=6).
Cf. A027801.
Sequence in context: A027441 A000971 A061927 this_sequence A084899 A074443 A007227
Adjacent sequences: A051920 A051921 A051922 this_sequence A051924 A051925 A051926
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KEYWORD
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easy,nonn
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AUTHOR
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Barry E. Williams, Dec 19 1999
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