Number of nondecreasing integer sequences of length 49 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) =53361a(16) =88209a(17) =148225a(18) =240100a(19) =393129a(20) =627264a(21) =1004004a(22) =1575025a(23) =2480625a(24) =3833763a(25) =5934088a(26) =9060062a(27) =13823385a(28) =20838791a(29) =31403601