Making a Riemann Sums function with multiple n values

clc;clear;
fun = input('what is the function: ');
a = input('what is a: ');
b = input('what is b: ');
n = input('what is n: ');
N=length(n);
h = (b-a)/N;
sum = 0;
for j=1:N
    h(j) = (b-a)/n(j);
    sum(j) =fun(a+h(j)*(j-1));
end
sum(n) = sum(n).*h(n);
disp(sum)

So, I am trying to create a Riemann sums function and want the final value to be an array of the chosen n values, e.g. n = 1:10. So, the values as you increase should become more accurate to the actual integral. But, When I look at the results, they just get smaller over time not even close to the actual value. When I was trying to find the integral with just 1 n, I got a pretty close value to the actual integral. I am not sure what I did wrong in converting it to an array format.