<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def nside_to_pixel_area(nside):
 """ Find the area of HEALPix pixels given the pixel dimensions of one of the 12 'top-level' HEALPix tiles. Parameters nside : int The number of pixels on the side of one of the 12 'top-level' HEALPix tiles. Returns ------- pixel_area : :class:`~astropy.units.Quantity` The area of the HEALPix pixels """

    nside = np.asanyarray(nside, dtype=np.int64)
    _validate_nside(nside)
    npix = 12 * nside * nside
    pixel_area = 4 * math.pi / npix * u.sr
    return pixel_area