Article date: Jul 1958
Article title: Some diverting tricks which involve the concept of numerical congruence
Mathematical Games column? Y
Book: 2. More Mathematical Puzzles and Diversions
Chapter: 4. Digital Roots
This data confirmed? yes
Notes
Peter Rowlett (27 August 2022):
Peter Rowlett initial guess (Very uncertain)
Peter Rowlett (26 October 2023):
I have seen this chapter and column side-by-side and they match.