191 (one hundred [and] ninety-one) is the natural number following 190 and preceding 192.
| ||||
|---|---|---|---|---|
| Cardinal | one hundred ninety-one | |||
| Ordinal | 191st (one hundred ninety-first) | |||
| Factorization | prime | |||
| Prime | 43rd | |||
| Greek numeral | ΡϞΑ´ | |||
| Roman numeral | CXCI | |||
| Binary | 101111112 | |||
| Ternary | 210023 | |||
| Senary | 5156 | |||
| Octal | 2778 | |||
| Duodecimal | 13B12 | |||
| Hexadecimal | BF16 | |||
In mathematics
edit191 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
editReferences
edit- ^ 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.
- ^ 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.
- ^ Wolfram MathWorld; Primitive Root
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