code: def window_blackman_nuttall(N):
      r
      a0 = 0.3635819
      a1 = 0.4891775
      a2 = 0.1365995
      a3 = 0.0106411
      return _coeff4(N, a0, a1, a2, a3)
docs: r"""Blackman Nuttall window
  
      returns a minimum, 4-term Blackman-Harris window. The window is minimum in the sense that its maximum sidelobes are minimized.
      The coefficients for this window differ from the Blackman-Harris window coefficients and produce slightly lower sidelobes.
  
      :param N: window length
  
      .. math:: w(n) = a_0 - a_1 \cos\left(\frac{2\pi n}{N-1}\right)+ a_2 \cos\left(\frac{4\pi n}{N-1}\right)- a_3 \cos\left(\frac{6\pi n}{N-1}\right)
  
      with :math:`a_0 = 0.3635819`, :math:`a_1 = 0.4891775`, :math:`a_2=0.1365995` and :math:`0_3=.0106411`
  
      .. plot::
          :width: 80%
          :include-source:
  
          from spectrum import window_visu
          window_visu(64, 'blackman_nuttall', mindB=-80)
  
      .. seealso:: :func:`spectrum.window.create_window`
      .. seealso:: :func:`create_window`, :class:`Window`