Article date: Feb 1981
Article title: Gauss's congruence theory was mod as early as 1801
Mathematical Games column? Y
Book: 15. The Last Recreations: Hydras, Eggs, and Other Mathematical Mystifications
Chapter: 15. Modulo Arithmetic and Hummer’s Wicked Witch
This data confirmed? yes
Notes
Peter Rowlett (27 August 2022):
Peter Rowlett initial guess (Uncertain)
Peter Rowlett (5 November 2023):
I have seen this chapter and column side-by-side and they match.