Triangle read by rows, T(n, k) = [x^k] (-2)^n*GegenbauerC(n, -1/2, x).

Terms

a(0) =1a(1) =0a(2) =2a(3) =2a(4) =0a(5) =-2a(6) =0a(7) =-4a(8) =0a(9) =4a(10) =-2a(11) =0a(12) =12a(13) =0a(14) =-10a(15) =0a(16) =12a(17) =0a(18) =-40a(19) =0a(20) =28a(21) =4a(22) =0a(23) =-60a(24) =0a(25) =140a(26) =0a(27) =-84a(28) =0a(29) =-40