E.g.f. 1/(1-3x-x^2).A052595E.g.f. 1/(1-3x-x^2).Terms a(0) =1a(1) =3a(2) =20a(3) =198a(4) =2616a(5) =43200a(6) =856080a(7) =19792080a(8) =522950400a(9) =15544690560a(10) =513406252800External referencesoeis: A052595