1. Division of Electronics and Information Engineering, Chonbuk National University, Jeonju, Republic of Korea;2. Department of Analysis, Institute of Mathematics, Budapest University of Technology and Economics, Budapest, Hungary
Abstract:
In this paper, we introduce modular symmetric designs and use them to study the existence of Hadamard matrices modulo 5. We prove that there exist 5‐modular Hadamard matrices of order n if and only if or . In particular, this solves the 5‐modular version of the Hadamard conjecture.