a(n) = n^2*(2*n^2 - 1); also Sum_{k=0..n-1} (2k+1)^3.

Terms

a(0) =0a(1) =1a(2) =28a(3) =153a(4) =496a(5) =1225a(6) =2556a(7) =4753a(8) =8128a(9) =13041a(10) =19900a(11) =29161a(12) =41328a(13) =56953a(14) =76636a(15) =101025a(16) =130816a(17) =166753a(18) =209628a(19) =260281a(20) =319600a(21) =388521a(22) =468028a(23) =559153a(24) =662976a(25) =780625a(26) =913276a(27) =1062153a(28) =1228528a(29) =1413721