import math


def some_function(n: float) -> float:
    """
    An approximation of the gamma function.

    >>> round(some_function(4), 3)
    24.0
    """
    s = sum(
        (
            1,
            1/((2**1)*(6*n)**1),
            1/((2**3)*(6*n)**2),
            -139/((2**3)*(2*3*5)*(6*n)**3),
            -571/((2**6)*(2*3*5)*(6*n)**4),
        )
    )
    return math.sqrt(2*math.pi*n)*(n/math.e)**n*s