G.f.: Product_{k>=1} 1/(1-x^k)^(3*k).

Terms

a(0) =1a(1) =3a(2) =12a(3) =37a(4) =111a(5) =303a(6) =804a(7) =2022a(8) =4950a(9) =11715a(10) =27081a(11) =61083a(12) =135112a(13) =293142a(14) =625620a(15) =1314267a(16) =2722323a(17) =5564172a(18) =11234865a(19) =22424904a(20) =44284545a(21) =86573147a(22) =167648418a(23) =321746907a(24) =612274678a(25) =1155782109a(26) =2165116416a(27) =4026391221a(28) =7435806048a(29) =13641093684