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Nth Tetrahedral Number

A tetrahedral number, or triangular pyramidal number, represents the number of spheres in a tetrahedron (a pyramid with a triangular base). The nth tetrahedral number can be calculated using the formula:

\[
T(n) = \frac{n \cdot (n + 1) \cdot (n + 2)}{6}
\]

Write a Python function `tetrahedral_number(n)` that takes an integer `n` as input and returns the nth tetrahedral number.

#### Example Usage
```python [main.nopy]
print(tetrahedral_number(1))  # Output: 1
print(tetrahedral_number(4))  # Output: 20
print(tetrahedral_number(5))  # Output: 35
```

#### Constraints
- The input `n` will be a positive integer.
- The function should return an integer value.
def tetrahedral_number(n):
    """
    Calculate the nth tetrahedral number.

    Args:
        n (int): The position of the tetrahedral number to calculate.

    Returns:
        int: The nth tetrahedral number.
    """
    # Implement the formula for the nth tetrahedral number
    pass