Number of nondecreasing integer sequences of length 27 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) =18224a(14) =30968a(15) =53323a(16) =88070a(17) =147791a(18) =238887a(19) =390019a(20) =619851a(21) =987327a(22) =1539460a(23) =2407824a(24) =3690457a(25) =5659994a(26) =8550843a(27) =12897622a(28) =19194188a(29) =28531103