161 (one hundred
ndsixty-one) 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
160 and preceding
162.
In mathematics
* 161 is the sum of five consecutive
prime number
A prime number (or a prime) is a natural number greater than 1 that is not a Product (mathematics), 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 ...
s:
23,
29,
31,
37, and
41.
* 161 is a
hexagonal pyramidal number.
* 161 is a
semiprime
In mathematics, a semiprime is a natural number that is the product of exactly two prime numbers. The two primes in the product may equal each other, so the semiprimes include the squares of prime numbers.
Because there are infinitely many prime n ...
. Since its prime factors
7 and
23 are both
Gaussian prime
In number theory, a Gaussian integer is a complex number whose real and imaginary parts are both integers. The Gaussian integers, with ordinary addition and multiplication of complex numbers, form an integral domain, usually written as \mathbf /ma ...
s, 161 is a
Blum integer.
* 161 is a
palindromic number
A palindromic number (also known as a numeral palindrome or a numeric palindrome) is a number (such as 16361) that remains the same when its digits are reversed. In other words, it has reflectional symmetry across a vertical axis. The term ''palin ...
.
* is a commonly used rational approximation of the
square root of 5
The square root of 5 is the positive real number that, when multiplied by itself, gives the prime number 5. It is more precisely called the principal square root of 5, to distinguish it from the negative number with the same property. This numbe ...
and is the closest fraction with denominator <300 to that number.
In other fields
* 161 as a code for
Anti-Fascist Action
Anti-Fascist Action (AFA) was a militant anti-fascist organisation, founded in the UK in 1985 by a wide range of anti-racist and anti-fascist organisations.
It was active in fighting far-right organisations, particularly the National Front a ...
(A=1, F=6, by order of the alphabet), sometimes used in ''161>88''
(''88'' being code for ''Heil Hitler'' among
neo-nazis
Neo-Nazism comprises the post–World War II militant, social, and political movements that seek to revive and reinstate Nazi ideology. Neo-Nazis employ their ideology to promote hatred and racial supremacy (often white supremacy), to att ...
, as H=8)
External links
Number Facts and Trivia: 161The Number 161
References
{{DEFAULTSORT:161 (Number)
Integers