n*(n-1)*(n^2-n+4)/6.

Terms

a(0) =0a(1) =0a(2) =2a(3) =10a(4) =32a(5) =80a(6) =170a(7) =322a(8) =560a(9) =912a(10) =1410a(11) =2090a(12) =2992a(13) =4160a(14) =5642a(15) =7490a(16) =9760a(17) =12512a(18) =15810a(19) =19722a(20) =24320a(21) =29680a(22) =35882a(23) =43010a(24) =51152a(25) =60400a(26) =70850a(27) =82602a(28) =95760a(29) =110432