Number of nondecreasing integer sequences of length 31 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) =1764a(10) =3136a(11) =5929a(12) =10201a(13) =18225a(14) =30976a(15) =53360a(16) =88201a(17) =148187a(18) =239961a(19) =392695a(20) =626049a(21) =1000876a(22) =1567506a(23) =2463530a(24) =3796803a(25) =5857417a(26) =8907047a(27) =13527344a(28) =20282712a(29) =30383074