Modular arithmetic is based on a number's remainder after division
by a divisor (called the modulus).
For an explanation and exercises, see Modular
Arithmetic, and More
Further discussion and activities can be found at Clock
Arithmetic Pages (the Number
Bracelet activity makes for an interesting research investigation).
For a more technical discussion, see Modular
Arithmetic and its interactive
modular arithmetic table. Notation note:
means that a divides p (and implies that p
is congruent to 0 (mod a)).