set term post enh font "Times,10" size 4.8,3.6 port 
set out "sum.eps"
I = {0,1}
f(x,n) = 1 + sum [k = 1:n] ((I*x)**k)/k!
unset key
set xrange [0:3*pi]
set yrange [-2:2]
plot for [i = 1:5] j=5*i real(f(x,j)) lw 2

!gv sum.eps
!convert -density 100 sum.eps sum.png