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645

645 is the natural number that follows 644 and precedes 646. In mathematics it factors as 3 × 5 × 43 and has eight positive divisors: 1, 3, 5, 15, 43, 129, 215, and 645. The sum of its digits is 15, so it is divisible by 3, and it ends in 5, so it is divisible by 5. In Roman numerals it is written as DCXLV. In binary it is 1010000101, and in hexadecimal it is 0x285.

In photography, 645 refers to a medium-format film frame size of 6 cm by 4.5 cm (commonly

Historically, 645 is associated with the year AD 645 in the early medieval period. In Japan, the

written
as
6x4.5).
This
format
sits
between
35mm
and
larger
formats
and
is
widely
used
in
cameras
designed
for
120-format
film,
such
as
Pentax
645,
Mamiya
645,
Contax
645,
and
Hasselblad
645-series
systems.
A
120
roll
can
yield
about
15
frames
in
6x4.5
format,
depending
on
the
camera
and
spacing,
making
it
a
popular
choice
for
a
balance
of
portability
and
image
quality.
Isshi
Incident
of
645
led
to
the
downfall
of
the
Soga
clan
and
prompted
the
Taika
Reforms,
which
reorganized
government
toward
centralized
rule
under
the
emperor
and
laid
groundwork
for
subsequent
legal
and
administrative
systems.
The
year
is
also
noted
in
chronicles
for
its
role
in
shaping
the
political
landscape
of
the
Asuka
period.