Some counting formulas for λ-quiddities over the rings Z/2ᵐZ

The λ-quiddities of size n are n-tuples of elements of a fixed set, solutions of a matrix equation appearing in the study of Coxeter's friezes. Their number and their properties are closely linked to the structure and the cardinality of the chosen set. The main objective of this text is to obtain an explicit formula giving the number of λ-quiddities of odd size, and a lower and upper bound for the number of λ-quiddities of even size, over the rings Z/2ᵐZ (m ≥ 2). We also give explicit formulas concerning the number of λ-quiddities of size n over Z/8Z.