# import necessary libraries
import pandas as pd
import numpy as np

# define your series and bins
bins = 10
series = pd.Series([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,\
                    12, 13, 14, 15, 16, 17, 18, 19, 20])

# use np.histogram method
hist, bin_edges = np.histogram(series, bins=bins)

# create a dataframe to better display the results
result_df = pd.DataFrame({'bin_lower': bin_edges[:-1], 
                          'bin_upper': bin_edges[1:], 
                          'frequency': hist})

# display result
print(result_df)