a(n) = n*(n+1)*(n^2+5*n+18)/24.

Terms

a(0) =2a(1) =8a(2) =21a(3) =45a(4) =85a(5) =147a(6) =238a(7) =366a(8) =540a(9) =770a(10) =1067a(11) =1443a(12) =1911a(13) =2485a(14) =3180a(15) =4012a(16) =4998a(17) =6156a(18) =7505a(19) =9065a(20) =10857a(21) =12903a(22) =15226a(23) =17850a(24) =20800a(25) =24102a(26) =27783a(27) =31871a(28) =36395a(29) =41385