G.f. A(x) satisfies: A(x) = 1 + x * A(x) / (1 + 3 * x * A(x)).

Terms

a(0) =1a(1) =1a(2) =-2a(3) =1a(4) =10a(5) =-38a(6) =28a(7) =289a(8) =-1262a(9) =1054a(10) =11044a(11) =-51302a(12) =45604a(13) =482068a(14) =-2319176a(15) =2140129a(16) =22753378a(17) =-111964106a(18) =105927508a(19) =1130780062a(20) =-5652760340a(21) =5444054956a(22) =58291068808a(23) =-294808277414a(24) =287740874260