G.f.: x^2*(1-2*x)/(1-8*x+22*x^2-26*x^3+14*x^4-5*x^5+x^6).

Terms

a(0) =0a(1) =0a(2) =1a(3) =6a(4) =26a(5) =102a(6) =386a(7) =1441a(8) =5353a(9) =19854a(10) =73612a(11) =272940a(12) =1012137a(13) =3753696a(14) =13922343a(15) =51640040a(16) =191546040a(17) =710504359a(18) =2635506573a(19) =9776051185a(20) =36263011505a(21) =134513166002a(22) =498960289449