What are the divisors of 1217?

1, 1217

There is a total of 2 positive divisors.
The sum of these divisors is 1218.
The arithmetic mean is 609.

2 odd divisors

1, 1217

How to compute the divisors of 1217?

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 1217 by each of the numbers from 1 to 1217 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)

1217 / 1 = 1217 (the remainder is 0, so 1 is a divisor of 1217)
1217 / 2 = 608.5 (the remainder is 1, so 2 is not a divisor of 1217)
1217 / 3 = 405.66666666667 (the remainder is 2, so 3 is not a divisor of 1217)
...
1217 / 1216 = 1.0008223684211 (the remainder is 1, so 1216 is not a divisor of 1217)
1217 / 1217 = 1 (the remainder is 0, so 1217 is a divisor of 1217)

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 1217 (i.e. 34.885527085025). 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 $\frac{N}{d} = D$ )

1217 / 1 = 1217 (the remainder is 0, so 1 and 1217 are divisors of 1217)
1217 / 2 = 608.5 (the remainder is 1, so 2 is not a divisor of 1217)
1217 / 3 = 405.66666666667 (the remainder is 2, so 3 is not a divisor of 1217)
...
1217 / 33 = 36.878787878788 (the remainder is 29, so 33 is not a divisor of 1217)
1217 / 34 = 35.794117647059 (the remainder is 27, so 34 is not a divisor of 1217)