What are the divisors of 1409?

1, 1409

There is a total of 2 positive divisors.
The sum of these divisors is 1410.
The arithmetic mean is 705.

2 odd divisors

1, 1409

How to compute the divisors of 1409?

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 1409 by each of the numbers from 1 to 1409 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)

1409 / 1 = 1409 (the remainder is 0, so 1 is a divisor of 1409)
1409 / 2 = 704.5 (the remainder is 1, so 2 is not a divisor of 1409)
1409 / 3 = 469.66666666667 (the remainder is 2, so 3 is not a divisor of 1409)
...
1409 / 1408 = 1.0007102272727 (the remainder is 1, so 1408 is not a divisor of 1409)
1409 / 1409 = 1 (the remainder is 0, so 1409 is a divisor of 1409)

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 1409 (i.e. 37.536648758247). 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 $\frac{N}{d} = D$ )

1409 / 1 = 1409 (the remainder is 0, so 1 and 1409 are divisors of 1409)
1409 / 2 = 704.5 (the remainder is 1, so 2 is not a divisor of 1409)
1409 / 3 = 469.66666666667 (the remainder is 2, so 3 is not a divisor of 1409)
...
1409 / 36 = 39.138888888889 (the remainder is 5, so 36 is not a divisor of 1409)
1409 / 37 = 38.081081081081 (the remainder is 3, so 37 is not a divisor of 1409)