What are the divisors of 1381?

1, 1381

There is a total of 2 positive divisors.
The sum of these divisors is 1382.
The arithmetic mean is 691.

2 odd divisors

1, 1381

How to compute the divisors of 1381?

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 1381 by each of the numbers from 1 to 1381 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)

1381 / 1 = 1381 (the remainder is 0, so 1 is a divisor of 1381)
1381 / 2 = 690.5 (the remainder is 1, so 2 is not a divisor of 1381)
1381 / 3 = 460.33333333333 (the remainder is 1, so 3 is not a divisor of 1381)
...
1381 / 1380 = 1.0007246376812 (the remainder is 1, so 1380 is not a divisor of 1381)
1381 / 1381 = 1 (the remainder is 0, so 1381 is a divisor of 1381)

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 1381 (i.e. 37.161808352124). 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 $\frac{N}{d} = D$ )

1381 / 1 = 1381 (the remainder is 0, so 1 and 1381 are divisors of 1381)
1381 / 2 = 690.5 (the remainder is 1, so 2 is not a divisor of 1381)
1381 / 3 = 460.33333333333 (the remainder is 1, so 3 is not a divisor of 1381)
...
1381 / 36 = 38.361111111111 (the remainder is 13, so 36 is not a divisor of 1381)
1381 / 37 = 37.324324324324 (the remainder is 12, so 37 is not a divisor of 1381)