(-1)^2*x^2,(-1)^(2+1)*(2*2-1)x^(2*2),(-1)^(3+1)*(2*3-1)*x^(2*3),(-1)^(4+1)*(2*4-1)x^(2*4),.(-1)^(n+1)*(2n-1)*x^(2n)