What is the 1991st prime number?
The 1991st prime number is 17321. The next prime is 17327 (a gap of 6) and the one before is 17317.
Position
Pick any whole number from 1 to 10,000.
How to work it out
- 1
List the primes in order: 2, 3, 5, 7, 11, 13, ā¦ The 1991st one is 17321.
- 2
17321 is prime because no prime up to ā17321 ā 131.61 divides it.
- 3
The primes are spread thinner as numbers grow: by the prime number theorem the 1991st prime is close to 1991 Ć ln(1991) ā 15124, and here it is 17321.
- 4
17321 has no twin: neither 17319 nor 17323 is prime.
Primes around the 1991st
| Position | Prime | Gap from the previous |
|---|---|---|
| 1988 | 17293 | 2 |
| 1989 | 17299 | 6 |
| 1990 | 17317 | 18 |
| 1991 | 17321 | 4 |
| 1992 | 17327 | 6 |
| 1993 | 17333 | 6 |
| 1994 | 17341 | 8 |
Questions
What is the 1991st prime number?
17321.
Which prime number is 17321?
17321 is the 1991st prime number.
What is the sum of the first 1991 primes?
16,118,380.