Number of nondecreasing arrangements of n numbers in -7..7 with sum zero.

Terms

a(0) =1a(1) =8a(2) =32a(3) =126a(4) =414a(5) =1242a(6) =3370a(7) =8512a(8) =20094a(9) =44916a(10) =95514a(11) =194668a(12) =381676a(13) =723354a(14) =1328980a(15) =2374753a(16) =4136477a(17) =7040196a(18) =11728606a(19) =19159798a(20) =30734578a(21) =48479188a(22) =75277670a(23) =115195490a(24) =173885716a(25) =259140928a(26) =381577586a(27) =555546058a(28) =800247348