A combinatorial survey of identities for the double factorial

By David Callan. 2009

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We survey combinatorial interpretations of some dozen identities for the double factorial such as, for instance, (2n-2)!! + Sum_{k=2}^{n} (2n-1)!!(2k-4)!!/(2k-1)!! = (2n-1)!!. Our methods are mostly bijective.

View Paper: https://www.semanticscholar.org/paper/63144f10e1d8644b62dea06132233afb69d93793