+**400** is the [natural number](/wiki/Natural_number) following 399 and preceding 401. A perfect square (20 x 20), it holds significance across [mathematics](/wiki/Mathematics) and various systems of measurement, often marking a notable quantity or historical period.
+## See also
+- [Number](/wiki/Number)
+- [Square Number](/wiki/Square_Number)
+- [Century](/wiki/Century)
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