2253801941domain: NAppears in sequencesExpansion of e.g.f. exp(-x)/(1-2*x).at n=10A000354Numerators of convergents to 1 + 2/(3 + 4/(5 + 6/(7 + ...))).at n=9A113012Double subfactorials: a(n) = (-1)^floor(n/2) * n!! * Sum_{i=0..floor(n/2)} (-1)^i/(n-2*i)!!.at n=20A334578