Number of zero-sum -n..n arrays of 4 elements with first and second differences also in -n..n.

Terms

a(0) =3a(1) =19a(2) =45a(3) =95a(4) =173a(5) =285a(6) =431a(7) =633a(8) =879a(9) =1183a(10) =1557a(11) =1999a(12) =2509a(13) =3117a(14) =3803a(15) =4581a(16) =5471a(17) =6463a(18) =7557a(19) =8791a(20) =10137a(21) =11609a(22) =13235a(23) =14997a(24) =16895a(25) =18975a(26) =21201a(27) =23587a(28) =26169a(29) =28921