# import necessary libraries
import pandas as pd
# create your sample series
series = pd.Series([1, 3, 6, 10, 15, 21])
# find diff of diff by list comprehension
differences = [series[i+1] - series[i]
for i in range(len(series)-1)]
diff_of_diffs = [differences[i+1] - differences[i]
for i in range(len(differences)-1)]
# print results
print(diff_of_diffs)