Question: Having problems plotting a discrete plot for the CDF of a Poisson distribution

I'm having problems trying to plot a discrete plot for a Poisson Distribution CDF.  I followed a model found elsewhere that someone had used to do a discrete plot of a sum.  The OP, in that case, was looking to plot a partial sum of:


The solution that was suggested to the OP was the following:

f[N1_]=sum[1/(n^3*sin^2[n]), {n,1,N1}];
DiscretePlot[f[x], {x,0,400},PlotRange->All];

Using that solution as a guide, I tried this:

lambda := 15.4;
f[N1_] = sum[exp(-lambda)*lambda^n/n!, {0, N1, n}];
DiscretePlot[f[x], {0, 50, x}, PlotRange -> All];

In the attached image, you can see the output from my attempt.

I am completely flummoxed. Any suggestions would be greatly appreciated.

Please Wait...