G.f. satisfies A(x) = (1 + x) * (1 + x/A(x)).

Terms

a(0) =1a(1) =2a(2) =-1a(3) =3a(4) =-10a(5) =36a(6) =-137a(7) =543a(8) =-2219a(9) =9285a(10) =-39587a(11) =171369a(12) =-751236a(13) =3328218a(14) =-14878455a(15) =67030785a(16) =-304036170a(17) =1387247580a(18) =-6363044315a(19) =29323149825a(20) =-135700543190a(21) =630375241380