Fifty-five

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:

• The atomic number of cesium.
• The number of delegates who attended the Constitutional Convention.
• In gallons, a common size of drum containing liquids.
• In miles per hour in many states of the United States, a common speed limit; it was the national speed limit for a time during the Energy Crisis of the late 1970s.
• In years of marriage, the emerald wedding anniversary.
• The code for international direct dial phone calls to Brazil.
• The designation of United States Interstate 55, a freeway that runs from Louisiana to Illinois.