191 (one hundred
ndninety-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
190 and preceding
192.
In mathematics
191 is a
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 ...
, part of a
prime quadruplet of four
primes: 191,
193
Year 193 ( CXCIII) was a common year starting on Monday of the Julian calendar. At the time, it was known as the Year of the Consulship of Sosius and Ericius (or, less frequently, year 946 ''Ab urbe condita''). The denomination 193 for this ye ...
,
197, and
199
Year 199 ( CXCIX) was a common year starting on Monday of the Julian calendar. At the time, it was sometimes known as year 952 ''Ab urbe condita''. The denomination 199 for this year has been used since the early medieval period, when the Anno ...
. Because doubling and adding one produces another prime number (383), 191 is a
Sophie Germain prime
In number theory, a prime number ''p'' is a if 2''p'' + 1 is also prime. The number 2''p'' + 1 associated with a Sophie Germain prime is called a . For example, 11 is a Sophie Germain prime and 2 × 11 +&nbs ...
. It is the smallest prime that is not a
full repetend prime in ''any'' base from 2 to 10; in fact, the smallest base for which 191 is a full period prime is
base 19
There are many different numeral systems, that is, writing systems for expressing numbers.
By culture / time period
"A ''base'' is a natural number B whose ''powers'' (B multiplied by itself some number of times) are specially designated wit ...
.
[Wolfram MathWorld]
Primitive Root
/ref>
See also
* 191 (disambiguation)
References
Integers
{{num-stub