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

Terms

a(0) =0a(1) =1a(2) =5a(3) =15a(4) =34a(5) =65a(6) =111a(7) =175a(8) =260a(9) =369a(10) =505a(11) =671a(12) =870a(13) =1105a(14) =1379a(15) =1695a(16) =2056a(17) =2465a(18) =2925a(19) =3439a(20) =4010a(21) =4641a(22) =5335a(23) =6095a(24) =6924a(25) =7825a(26) =8801a(27) =9855a(28) =10990a(29) =12209