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For the year A.D. 55, see 55.

Fifty-five (55, LV) is the natural number following fifty-four and preceeding fifty-six. It is a triangular number, made up of the numbers 1 to 10 added up, and it is also the sum of the squares of the integers 1 to 5. It is also a Fibonacci number. Its divisors are 1, 5, 11, and 55; its factorisation is

Fifty-five is also: