Number of zero-sum -n..n arrays of 4 elements with adjacent element differences also in -n..n.

Terms

a(0) =7a(1) =31a(2) =81a(3) =171a(4) =309a(5) =509a(6) =779a(7) =1133a(8) =1579a(9) =2131a(10) =2797a(11) =3591a(12) =4521a(13) =5601a(14) =6839a(15) =8249a(16) =9839a(17) =11623a(18) =13609a(19) =15811a(20) =18237a(21) =20901a(22) =23811a(23) =26981a(24) =30419a(25) =34139a(26) =38149a(27) =42463a(28) =47089a(29) =52041