G.f.: (3-4*x-3*x^2)/(1-2*x-3*x^2+2*x^3).

Terms

a(0) =3a(1) =2a(2) =10a(3) =20a(4) =66a(5) =172a(6) =502a(7) =1388a(8) =3938a(9) =11036a(10) =31110a(11) =87452a(12) =246162a(13) =692460a(14) =1948502a(15) =5482060a(16) =15424706a(17) =43398588a(18) =122107174a(19) =343560700a(20) =966645746a(21) =2719759244a(22) =7652334326a(23) =21530654892a(24) =60578794274a(25) =170444884572a(26) =479564842182