Number of nondecreasing arrangements of n numbers in -8..8 with sum zero.

Terms

a(0) =1a(1) =9a(2) =41a(3) =177a(4) =649a(5) =2137a(6) =6375a(7) =17575a(8) =45207a(9) =109583a(10) =252117a(11) =553981a(12) =1168261a(13) =2374753a(14) =4669367a(15) =8908546a(16) =16535154a(17) =29927526a(18) =52925886a(19) =91617530a(20) =155484150a(21) =259062316a(22) =424306230a(23) =683919048a(24) =1085984406a(25) =1700352360a(26) =2627337510