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# What is the Greatest Common Divisor (GCD) of 21 and 81?

## What is the Greatest Common Divisor (GCD)?

The greatest common divisor (GCD) of two or more numbers is the largest positive integer that evenly divides all the numbers. The GCD is also known as the highest common factor (HCF) or the greatest common factor (GCF).

## Finding the GCD of 21 and 81

When finding the GCD of two numbers, it is best to use the Euclidean algorithm, which is a method of finding the GCD of two or more numbers. To find the GCD of 21 and 81, we will use the Euclidean algorithm.

First, we find the remainder of the larger number, 81, divided by the smaller number, 21. The remainder is 0, which means that 21 is the GCD of 21 and 81.

### Conclusion

The GCD of 21 and 81 is 21. This means that 21 is the largest positive integer that evenly divides both numbers.

### Summary

The GCD of two or more numbers is the largest positive integer that evenly divides all the numbers. The GCD of 21 and 81 is 21, which means that 21 is the largest positive integer that evenly divides both numbers. The Euclidean algorithm is the best way to find the GCD of two numbers.