What are the divisors of 1555?

1, 5, 311, 1555

There is a total of 4 positive divisors.
The sum of these divisors is 1872.
The arithmetic mean is 468.

4 odd divisors

1, 5, 311, 1555

How to compute the divisors of 1555?

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 1555 by each of the numbers from 1 to 1555 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)

1555 / 1 = 1555 (the remainder is 0, so 1 is a divisor of 1555)
1555 / 2 = 777.5 (the remainder is 1, so 2 is not a divisor of 1555)
1555 / 3 = 518.33333333333 (the remainder is 1, so 3 is not a divisor of 1555)
...
1555 / 1554 = 1.0006435006435 (the remainder is 1, so 1554 is not a divisor of 1555)
1555 / 1555 = 1 (the remainder is 0, so 1555 is a divisor of 1555)

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 1555 (i.e. 39.433488306261). 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 $\frac{N}{d} = D$ )

1555 / 1 = 1555 (the remainder is 0, so 1 and 1555 are divisors of 1555)
1555 / 2 = 777.5 (the remainder is 1, so 2 is not a divisor of 1555)
1555 / 3 = 518.33333333333 (the remainder is 1, so 3 is not a divisor of 1555)
...
1555 / 38 = 40.921052631579 (the remainder is 35, so 38 is not a divisor of 1555)
1555 / 39 = 39.871794871795 (the remainder is 34, so 39 is not a divisor of 1555)