Application: Divisibility criteria revisited
Let
where
are the digits. The following congruence conditions generalize some of the criteria given in §
1.7.1
.
mod 2
:
.
mod 3
:
.
mod 4
:
.
mod 5
:
.
mod 8
:
.
mod 9
:
.
For example,
.
mod 10
:
.
There are also conditions for
,
, and
but they are left as exercises.
David Joyner 2007-09-03