How about
a_n = (-1)^n / sqrt(n)
(source) For positive a_n there is no such sequence.
Next time, you might want to ask at math.SE.
solved sequence whose series is convergent, but square is not convergent [closed]
How about
a_n = (-1)^n / sqrt(n)
(source) For positive a_n there is no such sequence.
Next time, you might want to ask at math.SE.
solved sequence whose series is convergent, but square is not convergent [closed]