145700domain: NAppears in sequencesNumber of isolated vertices in all 3-noncrossing RNA structures on n vertices.at n=12A187255G.f.: (1 + x/(1 + x^2/(1 + x^3/(1 + x^4/(1 + ...))))) / (1 - x/(1 - x^2/(1 - x^3/(1 - x^4/(1 - ...))))), a continued fraction.at n=23A285636