57081024000domain: NAppears in sequencesLah numbers: a(n) = n! * binomial(n-1, 3)/4!.at n=9A001755E.g.f.: (1-2x-sqrt(1-4*x))*x^2/2.at n=11A052732E.g.f.: x^2*(1-sqrt(1-4*x))/2.at n=11A052733Number of labeled trees with n nodes and 3 leaves.at n=9A055315a(n) = n! a(n-1) / a(n-2), where a(0) = 1, a(1) = 1.at n=13A372993