Unbounded stability of two-term recurrence sequences modulo 2 k Walter Carlip, Eliot Jacobson (1996) Acta Arithmetica
Unextendible sequences in finite abelian groups. Zhuang, Jujuan (2008) The Electronic Journal of Combinatorics [electronic only]
Universal formulae of Euler-Fermat type for subsets of Zm. Stefan Schwarz (1995) Collectanea Mathematica