270060domain: NAppears in sequencesNumber of leftist trees with n leaves.at n=18A006196Series reversion of g.f. A(x) is -A(-x).at n=17A089796G.f. A(x,y) satisfies: x*y*A(x,y) = Sum_{n=-oo..+oo} (-1)^n * x^(n*(n+1)/2) * A(x,y)^n, with coefficients T(n,k) of x^n*y^k in A(x,y) given as a triangle read by rows.at n=50A355360