G.f.: A(x) = 1 + x*exp( Sum_{k>=1} [A(-(-1)^k*x) - 1]^k/k ).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =10a(6) =18a(7) =70a(8) =135a(9) =566a(10) =1134a(11) =4972a(12) =10206a(13) =46098a(14) =96228a(15) =443946a(16) =938223a(17) =4397730a(18) =9382230a(19) =44523232a(20) =95698746a(21) =458639492a(22) =991787004a(23) =4791683932a(24) =10413763542a(25) =50652087010a(26) =110546105292a(27) =540758574440