a(n) = n*(n^3-n^2+n+1)/2.

Terms

a(0) =0a(1) =1a(2) =7a(3) =33a(4) =106a(5) =265a(6) =561a(7) =1057a(8) =1828a(9) =2961a(10) =4555a(11) =6721a(12) =9582a(13) =13273a(14) =17941a(15) =23745a(16) =30856a(17) =39457a(18) =49743a(19) =61921a(20) =76210a(21) =92841a(22) =112057a(23) =134113a(24) =159276a(25) =187825a(26) =220051a(27) =256257a(28) =296758a(29) =341881