Number of nondecreasing integer sequences of length 19 with sum zero and sum of absolute values 2n.

Terms

a(0) =1a(1) =4a(2) =9a(3) =25a(4) =49a(5) =121a(6) =225a(7) =484a(8) =900a(9) =1763a(10) =3128a(11) =5891a(12) =10062a(13) =17795a(14) =29809a(15) =50475a(16) =81654a(17) =134082a(18) =211205a(19) =335898a(20) =518266a(21) =801010a(22) =1208345a(23) =1828868a(24) =2704223a(25) =4001769a(26) =5820875a(27) =8453498a(28) =12088586a(29) =17274220