An alternating series is a special kind of series of the form
ββπ=1(β1)πβ1ππ
where ππ>0 for all πββ.
Such series exhibit a number of special properties,
for example, if ππ is non-increasing,
the Test for divergence by sequence limit is made stronger
giving the Alternating series test.
In cases where the alternating series test holds
but the series ββπ=1ππ is divergent,
the alternating series is said to be conditionally convergent.