from matplotlib import pyplot as plt

f = lambda x_prev: 1/4 * (x - 3)
x = 0

reihe = [x]

for i in range(100):
    x = f(x)
    reihe.append(x)

plt.plot(reihe, marker='o', linestyle='-')
plt.title("Reihen Plot")
plt.xlabel("n")
plt.ylabel("x_n")
plt.grid()
plt.savefig("reihen_plot.png", dpi=500)