Number of nondecreasing integer sequences of length 30 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) =53358a(16) =88191a(17) =148151a(18) =239851a(19) =392395a(20) =625299a(21) =999124a(22) =1563656a(23) =2455480a(24) =3780743a(25) =5826519a(26) =8849597a(27) =13423122a(28) =20098272a(29) =30062630