55 (number)
Template:Infobox number 55 (fifty-five) is the natural number following 54 and preceding 56.
Mathematics
55 is:
- the 10th Fibonacci number<ref>Template:Cite web</ref> and the 10th triangular number,<ref>Template:Cite web</ref> The sum of 55's digits is also 10.
- the 5th heptagonal number,<ref>Template:Cite web</ref> the 5th square pyramidal number,<ref>Template:Cite web</ref> and the 4th centered nonagonal number.<ref>Template:Cite web</ref>
55 is also the 19th semiprime and the 15th squarefree semiprime,<ref>Template:Cite web</ref><ref>Template:Cite web</ref> as well as the 32nd nontotient number (including odd numbers > 1)<ref>Template:Cite web</ref> the 36th arithmetic number,<ref>Template:Cite web</ref> the 38th composite number<ref>Template:Cite web</ref> (where the abundance of 55 = - 38),<ref>Template:Cite web</ref> the 43rd deficient number,<ref>Template:Cite web</ref> the 45th trapezoidal number,<ref>Template:Cite web</ref> and the 49th polite number.<ref>Template:Cite web</ref>
In addition, the first 10 non-zero numbers added together equal 55. (1+2+3+4+5+6+7+8+9+10 = 55)
Transportation
- In the United States, the National Maximum Speed Law prohibited speed limits higher than Template:Convert from 1974 to 1987. The number 55 became a popular shorthand for the 55 mph speed limit. For example, a hand with a pair of fives in Texas hold'em poker is referred to as a "speed limit".<ref name="HoldemSecrets">Template:Cite web
</ref>