Plot the Wave function

I am trying to plot a wave function, which represnets a response of a string, as a function of x at each time of this set t = [0 0.0002 0.0004 0.0006]. The function is in a series form (which means that the wave function has three modes). Consider n = 1 to 3. I am not sure if I should use For loop twice here. Thank you

clc
clear all
syms n t x
n=10;
t = [ 0 0.0002 0.0004 0.0006];
for i=1:length(t)
    for j=1:n
 an = -4*251001*((sin(200*pi*i/501)+sin(100*pi*i/501))/(10*pi*(10000*i^2-251001)));
 f= an*sin(pi*x*i/0.501)*cos(pi*2000*t*i/0.501); 
 end

fplot(f)

end