478320domain: NAppears in sequencesTriangle T(n,k) of numbers of proper k-covers of an unlabeled n-set, k=1..2^n-2.at n=40A055127E.g.f. B(x) = 4 + Integral A(x)*C(x) dx such that C(x)^2 - B(x)^2 = 9 and B(x)^2 - A(x)^2 = 7.at n=5A323564