A system of congruences 
mod 
with 
is called a complete
residue system (or covering system) if every integer 
satisfies 
for at least one value of 
. A covering system in which each integer is covered by just
one congruence is called an exact covering system.
Exact Covering System
See also
Complete Residue SystemExplore with Wolfram|Alpha
References
Guy, R. K. "Exact Covering Systems." §F14 in Unsolved Problems in Number Theory, 2nd ed. New York: Springer-Verlag, pp. 253-256, 1994.Referenced on Wolfram|Alpha
Exact Covering SystemCite this as:
Weisstein, Eric W. "Exact Covering System." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ExactCoveringSystem.html