Correction: upon further reading I see that there are no transposed digits but the whole text is somewhat misleading

I'd expect to have the

• input in the first line, followed by the appropriate calculations,
• the first result in the second line
  and so on.

Python: The description and example contain two pairs of transposed digits ( 21 <-> 12)

• description: The text states "...of the elements of input X = [6, 9, 21] is detailed below:" but the code starts with X_1 = [6, 9, 12]
• example (in essence the same): we call solution([6, 9, 21]) #-> 9 but the detailed steps start with [6, 9, 12]

The code shown assumes the correct values