code: def nside_to_npix(nside):
      
      nside = np.asanyarray(nside, dtype=np.int64)
      _validate_nside(nside)
      return 12 * nside ** 2
docs: Find the number of pixels corresponding to a HEALPix resolution.
  
      Parameters
      ----------
      nside : int
          The number of pixels on the side of one of the 12 'top-level' HEALPix tiles.
  
      Returns
      -------
      npix : int
          The number of pixels in the HEALPix map.