What are the divisors of 1003?

1, 17, 59, 1003

There is a total of 4 positive divisors.
The sum of these divisors is 1080.
The arithmetic mean is 270.

4 odd divisors

1, 17, 59, 1003

How to compute the divisors of 1003?

A number N is said to be divisible by a number M (with M non-zero) if, when we divide N by M, the remainder of the division is zero.

$N mod M = 0$

Brute force algorithm

We could start by using a brute-force method which would involve dividing 1003 by each of the numbers from 1 to 1003 to determine which ones have a remainder equal to 0.

$Remainder = N - (M \times ⌊ \frac{N}{M} ⌋)$

(where $⌊ \frac{N}{M} ⌋$ is the integer part of the quotient)

1003 / 1 = 1003 (the remainder is 0, so 1 is a divisor of 1003)
1003 / 2 = 501.5 (the remainder is 1, so 2 is not a divisor of 1003)
1003 / 3 = 334.33333333333 (the remainder is 1, so 3 is not a divisor of 1003)
...
1003 / 1002 = 1.000998003992 (the remainder is 1, so 1002 is not a divisor of 1003)
1003 / 1003 = 1 (the remainder is 0, so 1003 is a divisor of 1003)

Improved algorithm using square-root

However, there is another slightly better approach that reduces the number of iterations by testing only integers less than or equal to the square root of 1003 (i.e. 31.670175244226). Indeed, if a number N has a divisor D greater than its square root, then there is necessarily a smaller divisor d such that:

$D \times d = N$

(thus, if $\frac{N}{D} = d$ , then $\frac{N}{d} = D$ )

1003 / 1 = 1003 (the remainder is 0, so 1 and 1003 are divisors of 1003)
1003 / 2 = 501.5 (the remainder is 1, so 2 is not a divisor of 1003)
1003 / 3 = 334.33333333333 (the remainder is 1, so 3 is not a divisor of 1003)
...
1003 / 30 = 33.433333333333 (the remainder is 13, so 30 is not a divisor of 1003)
1003 / 31 = 32.354838709677 (the remainder is 11, so 31 is not a divisor of 1003)