← 190 191 192 →
Cardinalone hundred ninety-one
Ordinal191st
(one hundred ninety-first)
Factorizationprime
Primeyes
Greek numeralΡϞΑ´
Roman numeralCXCI
Binary101111112
Ternary210023
Senary5156
Octal2778
Duodecimal13B12
HexadecimalBF16

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

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

References

  1. ^ Sloane, N. J. A. (ed.). "Sequence A136162 (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.). "Sequence A005384 (Sophie Germain primes p: 2p+1 is also prime)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  3. ^ Wolfram MathWorld; Primitive Root