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A052572
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E.g.f. (1+2x-2x^2)/(1-x)^2.
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1
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1, 4, 10, 36, 168, 960, 6480, 50400, 443520, 4354560, 47174400, 558835200, 7185024000, 99632332800, 1482030950400, 23538138624000, 397533007872000, 7113748561920000, 134449847820288000, 2676192208994304000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| a(n) equals the permanent of the (n+1) X (n+1) matrix whose entry directly below the entry in the top right corner is 3, and all of whose other entries are 1. [From John M. Campbell, (jmaxwellcampbell(AT)gmail.com), May 25, 2011]
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 515
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FORMULA
| E.g.f.: -(-2*x+2*x^2-1)/(-1+x)^2
Recurrence: {a(0)=1, a(1)=4, a(2)=10, (-n^2-5*n-4)*a(n)+(n+3)*a(n+1)=0}
(n+3)*n! for n>0.
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MAPLE
| spec := [S, {S=Prod(Union(Z, Z, Sequence(Z)), Sequence(Z))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Essentially twice A038720.
Sequence in context: A149185 A149186 A197552 * A079725 A154152 A025237
Adjacent sequences: A052569 A052570 A052571 * A052573 A052574 A052575
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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