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521

521 is a natural number that follows 520 and precedes 522. In decimal notation it is written as 521. It is a prime number and, when expressed in Roman numerals, it is DXXI. The sum of its digits is 8 and its digital root is 8.

In base representations, 521 equals 1000001001 in binary, 1011 in octal, and 0x209 in hexadecimal. As a

Beyond pure mathematics, 521 appears as an ordinary integer used in various contexts such as catalog numbers,

prime
congruent
to
1
modulo
4,
521
can
be
expressed
as
a
sum
of
two
squares:
20^2
+
11^2.
It
has
no
positive
divisors
other
than
1
and
itself.
identifiers,
or
years
(for
example,
the
year
521
CE).
It
has
no
widely
recognized
meaning
beyond
its
mathematical
properties,
though
it
features
in
number-theory
discussions
and
puzzle
contexts.