191 (number)

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← 190 191 192 →
Cardinal one hundred ninety-one
Ordinal 191st
(one hundred ninety-first)
Factorization prime
Prime 43rd
Greek numeral ΡϞΑ´
Roman numeral CXCI, 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 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. [3]

See also

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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