import numpy as np
import matplotlib.pyplot as plt

def x(n):
    return (1/n) * np.heaviside(n, 0.5)

n = np.arange(1,100)

y = x(n)

E_x_total = 0
E_x = np.zeros(len(y))

for i in range(len(y)):
    E_x_total += abs(y[i])**2
    E_x[i] = E_x_total

fig, ax = plt.subplots()
ax.scatter(n,y, label="$x[n]$")
ax.scatter(n, E_x, c='red', label="$E_x$")
ax.axhline(np.pi**2 / 6, linestyle='-', label="$\\frac{\pi^2}{6}$")
ax.legend()
plt.show()