Number of nondecreasing integer sequences of length 15 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) =483a(8) =892a(9) =1726a(10) =2999a(11) =5517a(12) =9136a(13) =15691a(14) =25423a(15) =41668a(16) =64943a(17) =102972a(18) =155880a(19) =238808a(20) =353814a(21) =525710a(22) =760658a(23) =1106657a(24) =1568464a(25) =2228879a(26) =3108245a(27) =4333985a(28) =5940271a(29) =8151896