G.f.: (1-x)^5/((-1+4*x-3*x^2+x^3)*(1-3*x+x^2)*(-1+2*x)).

Terms

a(0) =1a(1) =4a(2) =16a(3) =60a(4) =215a(5) =747a(6) =2539a(7) =8491a(8) =28049a(9) =91782a(10) =298109a(11) =962594a(12) =3093687a(13) =9905444a(14) =31619072a(15) =100681587a(16) =319944693a(17) =1015039586a(18) =3215903436a(19) =10177462312a(20) =32179381609a(21) =101668695088a(22) =321014982282