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9

Nine is a natural number that follows eight and precedes ten. In the base-10 numeric system it is the largest single-digit number. It is the first odd composite number and can be written as 3 squared (3^2).

In mathematics, nine has several notable properties. It is a perfect square and a composite number with

Science and technology note that nine is the atomic number of fluorine, a highly reactive halogen gas

Other common references include the nine-degree angle in geometry and the ninefold symmetry found in some cultural

positive
divisors
1,
3,
and
9.
The
digit-sum
property
of
multiples
of
nine
is
distinctive:
the
sum
of
the
digits
of
any
multiple
of
nine
is
itself
a
multiple
of
nine,
and
the
digital
root
of
these
numbers
is
nine.
In
various
bases,
nine
has
simple
representations:
in
binary
it
is
1001,
in
base-3
it
is
100,
in
base-8
it
is
11,
and
in
base-16
it
remains
9.
In
Roman
numerals
it
is
written
IX.
A
polygon
with
nine
sides
is
called
a
nonagon.
at
room
temperature.
Fluorine
forms
a
wide
range
of
compounds,
including
fluorides
used
in
dental
care
and
various
industrial
applications.
In
computing,
the
ASCII
code
9
represents
a
horizontal
tab.
artifacts.
The
number
appears
in
calendars,
timekeeping,
and
counting
systems
as
a
basic
unit
in
several
cultural
and
scientific
contexts,
making
it
a
familiar
and
frequently
encountered
integer
across
disciplines.