Coefficients of x/(1-3*x-3*x^2-x^3).

Terms

a(0) =0a(1) =1a(2) =3a(3) =12a(4) =46a(5) =177a(6) =681a(7) =2620a(8) =10080a(9) =38781a(10) =149203a(11) =574032a(12) =2208486a(13) =8496757a(14) =32689761a(15) =125768040a(16) =483870160a(17) =1861604361a(18) =7162191603a(19) =27555258052a(20) =106013953326a(21) =407869825737