class_docstr: Represents Fourier sine/cosine series.
  
  Explanation
  ===========
  
  This class only represents a fourier series.
  No computation is performed.
  
  For how to compute Fourier series, see the :func:`fourier_series`
  docstring.
  
  See Also
  ========
  
  sympy.series.fourier.fourier_series
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code: def an(self):
      return self.args[2][1]
  
imports: from sympy.core.numbers import oo, pi
  from sympy.core.symbol import Wild
  from sympy.core.expr import Expr
  from sympy.core.add import Add
  from sympy.core.containers import Tuple
  from sympy.core.singleton import S
  from sympy.core.symbol import Dummy, Symbol
  from sympy.core.sympify import sympify
  from sympy.functions.elementary.trigonometric import sin, cos, sinc
  from sympy.series.series_class import SeriesBase
  from sympy.series.sequences import SeqFormula
  from sympy.sets.sets import Interval
  from sympy.utilities.iterables import is_sequence
label_desc: Use image node_id 6 for calling the FourierSeries obj's underlying member method code with example usage: obj.an() and returns: self