### 6,531 and 1,947 are not coprime (relatively, mutually prime) if they have common prime factors, that is, if their greatest (highest) common factor (divisor), gcf, hcf, gcd, is not 1.

## Calculate the greatest (highest) common factor (divisor), gcf, hcf, gcd

### Approach 1. Integer numbers prime factorization:

#### Prime Factorization of a number: finding the prime numbers that multiply together to make that number.

#### 6,531 = 3 × 7 × 311;

6,531 is not a prime, is a composite number;

#### 1,947 = 3 × 11 × 59;

1,947 is not a prime, is a composite number;

#### Positive integers that are only dividing by themselves and 1 are called prime numbers. A prime number has only two factors: 1 and itself.

#### A composite number is a positive integer that has at least one factor (divisor) other than 1 and itself.

### Calculate greatest (highest) common factor (divisor):

#### Multiply all the common prime factors, by the lowest exponents (if any).

#### gcf, hcf, gcd (6,531; 1,947) = 3;

## Coprime numbers (relatively prime) (6,531; 1,947)? No.

The numbers have common prime factors.

gcf, hcf, gcd (1,947; 6,531) = 3.

### Approach 2. Euclid's algorithm:

#### This algorithm involves the operation of dividing and calculating remainders.

#### 'a' and 'b' are the two positive integers, 'a' >= 'b'.

#### Divide 'a' by 'b' and get the remainder, 'r'.

#### If 'r' = 0, STOP. 'b' = the GCF (HCF, GCD) of 'a' and 'b'.

#### Else: Replace ('a' by 'b') & ('b' by 'r'). Return to the division step above.

#### Step 1. Divide the larger number by the smaller one:

6,531 ÷ 1,947 = 3 + 690;

Step 2. Divide the smaller number by the above operation's remainder:

1,947 ÷ 690 = 2 + 567;

Step 3. Divide the remainder from the step 1 by the remainder from the step 2:

690 ÷ 567 = 1 + 123;

Step 4. Divide the remainder from the step 2 by the remainder from the step 3:

567 ÷ 123 = 4 + 75;

Step 5. Divide the remainder from the step 3 by the remainder from the step 4:

123 ÷ 75 = 1 + 48;

Step 6. Divide the remainder from the step 4 by the remainder from the step 5:

75 ÷ 48 = 1 + 27;

Step 7. Divide the remainder from the step 5 by the remainder from the step 6:

48 ÷ 27 = 1 + 21;

Step 8. Divide the remainder from the step 6 by the remainder from the step 7:

27 ÷ 21 = 1 + 6;

Step 9. Divide the remainder from the step 7 by the remainder from the step 8:

21 ÷ 6 = 3 + 3;

Step 10. Divide the remainder from the step 8 by the remainder from the step 9:

6 ÷ 3 = 2 + 0;

At this step, the remainder is zero, so we stop:

3 is the number we were looking for, the last remainder that is not zero.

This is the greatest common factor (divisor).

#### gcf, hcf, gcd (6,531; 1,947) = 3;

## Coprime numbers (relatively prime) (6,531; 1,947)? No.

gcf, hcf, gcd (1,947; 6,531) = 3.