Let the mean and the variance of 20 observations \(x_1, x_2,…., x_{20}\) be 15 and 9, respectively. For a ∈ R, if the mean of \((x_1 + α)^2, (x_2 + α)^2,….,(x_{20} + α)^2\) is 178, then the square of the maximum value of \(α\) is equal to ___________.