191 (number)

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← 190 191 192 →
Cardinal one hundred ninety-one
Ordinal 191st
(one hundred ninety-first)
Factorization prime
Prime yes
Greek numeral ΡϞΑ´
Roman numeral CXCI
Binary 101111112
Ternary 210023
Senary 5156
Octal 2778
Duodecimal 13B12
Hexadecimal BF16

191 (one hundred [and] ninety-one) is the natural number following 190 and preceding 192.

Contents

In mathematics

191 is a prime number, part of a prime quadruplet of four primes: 191, 193, 197, and 199. [1] Because doubling and adding one produces another prime number (383), 191 is a Sophie Germain prime. [2] It is the smallest prime that is not a full reptend prime in any base from 2 to 10; in fact, the smallest base for which 191 is a full period prime is base 19. [3]

See also

Related Research Articles

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600 is the natural number following 599 and preceding 601.

800 is the natural number following 799 and preceding 801.

900 is the natural number following 899 and preceding 901. It is the square of 30 and the sum of Euler's totient function for the first 54 positive integers. In base 10 it is a Harshad number. It is also the first number to be the square of a sphenic number.

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References

  1. ↑ Sloane, N. J. A. (ed.). "SequenceA136162(List of prime quadruplets {p, p+2, p+6, p+8})". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  2. ↑ Sloane, N. J. A. (ed.). "SequenceA005384(Sophie Germain primes p: 2p+1 is also prime)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  3. ↑ Wolfram MathWorld; Primitive Root


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