>>> from series12 import calc_term

--ini

>>> x = calc_term(0.1, 1, 0.1)
>>> x
0.1997

>>> x = calc_term(0.1, 2, 0.1997)
>>> x
-0.1987

>>> x = calc_term(0.1, 3, -0.1987)
>>> x
0.1987

--fi

>>> x = calc_term(1.0, 1, 1.0)
>>> x
1.6829

>>> x = calc_term(1.0, 2, 1.6829)
>>> x
-1.181

>>> x = calc_term(1.0, 3, -1.181)
>>> x
1.5664