整数的阶乘（factorial）是所有小于及等于该数的正整数的积，0的阶乘为1。即：n!=1×2×3×...×n。

import numpy as npimport matplotlib as mplimport matplotlib.pyplot as pltfrom scipy.special import gammafrom scipy.special import factorialmpl.rcParams['axes.unicode_minus'] = Falsempl.rcParams['font.sans-serif'] = 'SimHei'if __name__ == '__main__':    N = 5    x = np.linspace(0, N, 50)    y = gamma(x+1)    plt.figure(facecolor='w')    plt.plot(x, y, 'r-', x, y, 'm*', lw=2)    z = np.arange(0, N+1)    print z    f = factorial(z, exact=True)    # 阶乘    print f    plt.plot(z, f, 'go', markersize=8)    plt.grid(b=True)    plt.xlim(-0.1,N+0.1)    plt.ylim(0.5, np.max(y)*1.05)    plt.xlabel(u'X', fontsize=15)    plt.ylabel(u'Gamma(X) - 阶乘', fontsize=15)    plt.title(u'阶乘和Gamma函数', fontsize=16)    plt.show()