169 (one hundred
ndsixty-nine) is the natural number following
168 and preceding
170.
In mathematics
169 is an
odd number
In mathematics, parity is the property of an integer of whether it is even or odd. An integer is even if it is divisible by 2, and odd if it is not.. For example, −4, 0, and 82 are even numbers, while −3, 5, 23, and 69 are odd numbers.
The ...
, a
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 ...
, and a
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 ...
.
169 is a
square number
In mathematics, a square number or perfect square is an integer that is the square (algebra), square of an integer; in other words, it is the multiplication, product of some integer with itself. For example, 9 is a square number, since it equals ...
:
13 × 13 = 169, and if each number is reversed the equation is still true:
31 ×
31 = 961.
144 shares this property: 12 × 12 = 144, 21 × 21 = 441.
169 is one of the few squares to also be a
centered hexagonal number
In mathematics and combinatorics, a centered hexagonal number, or centered hexagon number, is a centered polygonal number, centered figurate number that represents a hexagon with a dot in the center and all other dots surrounding the center dot ...
.
Like all odd squares, it is a
centered octagonal number
A centered octagonal number is a centered number, centered figurate number that represents an octagon with a dot in the center and all other dots surrounding the center dot in successive octagonal layers.. The centered octagonal numbers are th ...
. 169 is an odd-indexed
Pell number, thus it is also a
Markov number, appearing in the solutions (2, 169, 985), (2, 29, 169), (29, 169, 14701), etc. 169 is the sum of seven consecutive
prime
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways ...
s:
13 +
17 +
19 +
23 +
29 +
31 +
37. 169 is a difference in consecutive cubes, equaling
In other fields
* 169 is known in the
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...
world as the first number of an
automatic IPv4 address assigned by
TCP/IP
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...
when no external
networking device is contactable
References
External links
Number Facts and Trivia: 169The Positive Integer 169The Number 169Number Gossip 169
{{DEFAULTSORT:169 (Number)
Integers