+55 is a [natural number](/wiki/natural-number) between 54 and 56. It is notable as the tenth [Fibonacci number](/wiki/Fibonacci_number) and the tenth triangular number, representing the sum of the first ten positive integers.
+## See also
+- [Triangular number](/wiki/triangular-number)
+- [Cesium](/wiki/cesium)
+- [Number theory](/wiki/number-theory)
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