Number of nondecreasing arrangements of n numbers in -6..6 with sum zero.

Terms

a(0) =1a(1) =7a(2) =25a(3) =86a(4) =252a(5) =676a(6) =1656a(7) =3788a(8) =8150a(9) =16660a(10) =32540a(11) =61108a(12) =110780a(13) =194668a(14) =332578a(15) =553981a(16) =901723a(17) =1437269a(18) =2247151a(19) =3451798a(20) =5216252a(21) =7764392a(22) =11396054a(23) =16509188a(24) =23626234a(25) =33427622a(26) =46791278a(27) =64841876a(28) =89008530a(29) =121095602