a(n) = (n/2)*(n + 1)*(3*n + 11).

Terms

a(0) =14a(1) =51a(2) =120a(3) =230a(4) =390a(5) =609a(6) =896a(7) =1260a(8) =1710a(9) =2255a(10) =2904a(11) =3666a(12) =4550a(13) =5565a(14) =6720a(15) =8024a(16) =9486a(17) =11115a(18) =12920a(19) =14910a(20) =17094a(21) =19481a(22) =22080a(23) =24900a(24) =27950a(25) =31239a(26) =34776a(27) =38570a(28) =42630a(29) =46965