Number of strictly increasing arrangements of 4 nonzero numbers in -(n+2)..(n+2) with sum zero.

Terms

a(0) =1a(1) =3a(2) =8a(3) =16a(4) =31a(5) =51a(6) =80a(7) =118a(8) =167a(9) =227a(10) =302a(11) =390a(12) =495a(13) =617a(14) =758a(15) =918a(16) =1101a(17) =1305a(18) =1534a(19) =1788a(20) =2069a(21) =2377a(22) =2716a(23) =3084a(24) =3485a(25) =3919a(26) =4388a(27) =4892a(28) =5435a(29) =6015