a(n) = (2*n^3 + 5*n^2 + 5*n)/2.

Terms

a(0) =6a(1) =23a(2) =57a(3) =114a(4) =200a(5) =321a(6) =483a(7) =692a(8) =954a(9) =1275a(10) =1661a(11) =2118a(12) =2652a(13) =3269a(14) =3975a(15) =4776a(16) =5678a(17) =6687a(18) =7809a(19) =9050a(20) =10416a(21) =11913a(22) =13547a(23) =15324a(24) =17250a(25) =19331a(26) =21573a(27) =23982a(28) =26564a(29) =29325