Sum of the partition parts of 3n into 3 parts.

Terms

a(0) =3a(1) =18a(2) =63a(3) =144a(4) =285a(5) =486a(6) =777a(7) =1152a(8) =1647a(9) =2250a(10) =3003a(11) =3888a(12) =4953a(13) =6174a(14) =7605a(15) =9216a(16) =11067a(17) =13122a(18) =15447a(19) =18000a(20) =20853a(21) =23958a(22) =27393a(23) =31104a(24) =35175a(25) =39546a(26) =44307a(27) =49392a(28) =54897a(29) =60750