I'm trying to plot the points (n, a(n)) from n=1 to n=20, but Maple's just telling me what I want to plot, without actually plotting it. Any ideas on what I'm doing wrong?

I'm trying to plot the points (n, a(n)) from n=1 to n=20, but Maple's just telling me what I want to plot, without actually plotting it. Any ideas on what I'm doing wrong?

The following syntax worked for me, which produces the graph shown.