13749310574domain: NAppears in sequencesa(n) = n!! - 1.at n=21A128882G.f.: 1 + Sum_{n>=1} a(n)*x^n/(1 - x^n) = 1/(1 - x/(1 - 2*x/(1 - 3*x/(1 - 4*x/(1 - ...))))).at n=10A286310