An infinite series [math]\sum_{n=1}^{\infty}z_n[/math] of complex numbers converges to the sum [math]S[/math] if the sequence
[math]S_N=\sum_{n=1}^{N}z_n[/math] of partial sums converges to [math]S[/math]. We then write [math]\sum_{n=1}^{\infty}z_n=S[/math].
