Number of partitions of 3n in which every part is <=n.

Terms

a(0) =1a(1) =4a(2) =12a(3) =34a(4) =84a(5) =199a(6) =436a(7) =919a(8) =1845a(9) =3590a(10) =6751a(11) =12384a(12) =22142a(13) =38797a(14) =66634a(15) =112540a(16) =187013a(17) =306421a(18) =495332a(19) =791131a(20) =1249153a(21) =1951915a(22) =3019969a(23) =4630063a(24) =7037286a(25) =10610240a(26) =15874998a(27) =23582081a(28) =34791668a(29) =50999319