Returns the greatest common denominator of the two numbers a and b.

`gcd(a,b)`

The greatest common denominator function returns the largest shared denominator of the two integer inputs and .

```
gcd(6, 4) = 2
```

```
gcd(8, 12) = 2
```

```
gcd(12, 27) = 3
```

```
gcd(10, 15) = 5
```

```
gcd(12, 48) = 6
```

```
gcd(15, 25) = 5
```

```
gcd(100, 31) = 1
```