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A052887
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A simple grammar.
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1
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1, 0, 2, 12, 84, 720, 7320, 85680, 1130640, 16571520, 266747040, 4673592000, 88476252480, 1798674958080, 39061703640960, 902110060051200, 22068313153286400, 569874634276147200, 15486794507222438400
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| Categorize your books by the branch of mathematics that they concern (there may be any number of these). Within each category seperate the books you understand from the ones that you don't (there must be at least one book you understand and one that you don't). Linearly order both seperations of books in every category. - Geoffrey Critzer, Dec 11 2011
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 860
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FORMULA
| E.g.f.: exp(x^2/(-1+x)^2)
Recurrence: {a(1)=0, a(0)=1, a(2)=2, (-n^3-2*n-3*n^2)*a(n)+(3*n^2+7*n+2)*a(n+1)+(-6-3*n)*a(n+2)+a(n+3)}
Sum_{k=0..floor(n/2)} n!/k!*binomial(n-1, 2*k-1). - Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 13 2003
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MAPLE
| spec := [S, {B=Sequence(Z, 1 <= card), C=Prod(B, B), S= Set(C)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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MATHEMATICA
| nn = 20; a = x/(1 - x); Range[0, nn]! CoefficientList[Series[Exp[ a^2], {x, 0, nn}], x] (* Geoffrey Critzer, Dec 11 2011 *)
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PROG
| (Maxima) makelist(if n=0 then 1 else sum(n!/k!*binomial(n-1, 2*k-1), k, 0, floor(n/2)), n, 0, 18); [Bruno Berselli, May 25 2011]
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CROSSREFS
| Sequence in context: A130464 A006657 A105927 * A052867 A179495 A097237
Adjacent sequences: A052884 A052885 A052886 * A052888 A052889 A052890
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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