191 is a 3-digit prime number. 191 has 2 factors, 1 and 191. It is the 43rd prime number, and the eighteenth prime number from 101-200.
Proofs[]
— 191 is divisible by 1.
— 191 is not divisible by 2-190.
- — 191 is divisible by 191.
Therefore, 191 is a prime number.
As an Exponent of Mersenne Number[]
2191 - 1 is divisible by 383, 7,068,569,257, etc., and is therefore not a prime number.
Relationship with other odd numbers[]
The numbers before[]
- 179 is the second previous prime number.
- 181 is the prime number preceding 191.
- 183 is a composite number. Its prime factorization is 3 × 61.
- 185 is also a composite number. Its prime factorization is 5 × 37.
- 187 is another composite number. Its prime factorization is 11 × 17.
- 189 is yet another composite number. Its prime factorization is 33 × 7.
The numbers after[]
- 193 is the odd number and prime number following 191.
- The difference between 193 and 191 is 2. Therefore, they are twin primes.
- 195 is a composite number. Its prime factorization is 3 × 5 × 13.
- Notably, 195 is a sphenic number, since it has exactly three prime factors.
- 197 is the prime number following 193.
Trivia[]
- 191 is part of the prime quadruplet (191, 193, 197, 199).
- 191 is a Sophie Germain prime, since 191 × 2 + 1 = 383 is also prime.
- 191 is the smallest prime number that is not a full reptend prime in any base from base 2 to 10.