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Search: id:A027789
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| A027789 |
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2*(n+1)*binomial(n+3,4). |
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+0
3
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| 4, 30, 120, 350, 840, 1764, 3360, 5940, 9900, 15730, 24024, 35490, 50960, 71400, 97920, 131784, 174420, 227430, 292600, 371910, 467544, 581900, 717600, 877500, 1064700, 1282554, 1534680, 1824970, 2157600, 2537040, 2968064
(list; graph; listen)
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OFFSET
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0,1
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FORMULA
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Number of 8-subsequences of [ 1, n ] with just 3 contiguous pairs; g.f. 2*(2+3x)/(1-x)^6; 2*A006470.
C(n+2, 2)*C(n+4, 3) - Zerinvary Lajos (zlaja(AT)freemail.hu), May 10 2005
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MAPLE
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a:=n->(sum((numbperm(n, 4)), j=3..n)):seq(a(n)/12, n=4..34); [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Aug 26 2008]
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CROSSREFS
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Adjacent sequences: A027786 A027787 A027788 this_sequence A027790 A027791 A027792
Sequence in context: A014697 A027297 A027445 this_sequence A130424 A005715 A123351
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KEYWORD
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nonn,easy
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AUTHOR
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thi ngoc dinh (via rkg(AT)cpsc.ucalgary.ca)
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