Factors of 1991

The factors of 1991 are 1, 11, 181, 1991. It has 4 factors.

Factors of 1991

Pick any whole number from 1 to 10,000.

1991 = 11 \times 181

How to work it out

1
A factor of 1991 is a whole number that divides it with nothing left over. You only need to test the numbers up to √1991 ≈ 44.62; every one that divides gives a pair.
2
The factor pairs are listed in the table below. Together they give 4 factors.
3
Prime factorisation: keep dividing by the smallest prime that fits.
$1991 = 11 \times 181$
4
Add all the factors: 1 + 11 + 181 + 1991 = 2184. Without 1991 itself that is 193, so 1991 is a deficient number.

LaTeX source of the formulas on this page

\[ 1991 = 11 \times 181 \]

Factor	Pairs with	Product
1	1991	1 × 1991 = 1991
11	181	11 × 181 = 1991

What are the factors of 1991?

The factors of 1991 are 1, 11, 181, 1991. It has 4 factors.

What are the prime factors of 1991?

11, 181. As a product: 11 × 181.

How many factors does 1991 have?

1991 has 4 factors (2 factor pairs).

What is the sum of the factors of 1991?

2184.

Is 1991 a prime number?

No. It is divisible by 11, so 1991 = 11 × 181.