Expansion of g.f. x*(1-x)/(1-4*x-2*x^2+x^3).

Terms

a(0) =1a(1) =3a(2) =14a(3) =61a(4) =269a(5) =1184a(6) =5213a(7) =22951a(8) =101046a(9) =444873a(10) =1958633a(11) =8623232a(12) =37965321a(13) =167149115a(14) =735903870a(15) =3239948389a(16) =14264452181a(17) =62801801632a(18) =276496162501