Number of nondecreasing integer sequences of length 20 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) =3133a(11) =5911a(12) =10127a(13) =17976a(14) =30254a(15) =51476a(16) =83727a(17) =138214a(18) =219057a(19) =350478a(20) =544347a(21) =846845a(22) =1286514a(23) =1960520a(24) =2920291a(25) =4352663a(26) =6378968a(27) =9332660a(28) =13448845a(29) =19362348