def get_pascal_triangle_unique_coefficients(depth: int) -> set[int]:
    """
    Returns the unique coefficients of a Pascal's triangle of depth "depth".

    The coefficients of this triangle are symmetric. A further improvement to this
    method could be to calculate the coefficients once per level. Nonetheless,
    the current implementation is fast enough for the original problem.

    >>> get_pascal_triangle_unique_coefficients(1)
    {1}
    >>> get_pascal_triangle_unique_coefficients(2)
    {1}
    >>> get_pascal_triangle_unique_coefficients(3)
    {1, 2}
    >>> get_pascal_triangle_unique_coefficients(8)
    {1, 2, 3, 4, 5, 6, 7, 35, 10, 15, 20, 21}
    """
    coefficients = {1}
    previous_coefficients = [1]
    for step in range(2, depth + 1):
        coefficients_begins_one = previous_coefficients + [0]
        coefficients_ends_one = [0] + previous_coefficients
        previous_coefficients = []
        for x, y in zip(coefficients_begins_one, coefficients_ends_one):
            coefficients.add(x + y)
            previous_coefficients.append(x + y)
    return coefficients