a(n) = (n/4)*(n^3+2*n^2+5*n+8).

Terms

a(0) =0a(1) =4a(2) =17a(3) =51a(4) =124a(5) =260a(6) =489a(7) =847a(8) =1376a(9) =2124a(10) =3145a(11) =4499a(12) =6252a(13) =8476a(14) =11249a(15) =14655a(16) =18784a(17) =23732a(18) =29601a(19) =36499a(20) =44540a(21) =53844a(22) =64537a(23) =76751a(24) =90624a(25) =106300a(26) =123929a(27) =143667a(28) =165676a(29) =190124