55 (fifty-five) is the
natural number
In mathematics, the natural numbers are the numbers 0, 1, 2, 3, and so on, possibly excluding 0. Some start counting with 0, defining the natural numbers as the non-negative integers , while others start with 1, defining them as the positive in ...
following
54 and preceding
56.
Mathematics
55 is:
*the 10th
Fibonacci number
In mathematics, the Fibonacci sequence is a Integer sequence, sequence in which each element is the sum of the two elements that precede it. Numbers that are part of the Fibonacci sequence are known as Fibonacci numbers, commonly denoted . Many w ...
and the 10th
triangular number, The sum of 55's digits is also 10.
*the 5th
heptagonal number, the 5th
square pyramidal number, and the 4th
centered nonagonal number.
55 is also the 19th
semiprime and the 15th squarefree semiprime, as well as the 32nd
nontotient number (including odd numbers > 1) the 36th
arithmetic number, the 38th
composite number
A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Accordingly it is a positive integer that has at least one divisor other than 1 and itself. Every positive integer is composite, prime numb ...
(where the
abundance of 55 = - 38), the 43rd
deficient number
In number theory, a deficient number or defective number is a positive integer for which the sum of divisors of is less than . Equivalently, it is a number for which the sum of proper divisors (or aliquot sum) is less than . For example, th ...
, the 45th
trapezoidal number, and the 49th
polite number.
Transportation
*In the United States, the
National Maximum Speed Law prohibited speed limits higher than 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".
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References
{{Integers, zero
Integers