sum command...

[webmasterpdx]

Of course I'm exceeding CAS limits, but why is it calculating it as a ratio? I would imagine or want the SUM function to work like this pseudocode:
sum = 0;
for x=1 to 5000
sum = sum + expression;
endfor

Clearly, that's not how it's being evaluated....which is kinda weird.
I tried running this in home:
sum(1/x^2, x, 1, 1000)

It gave be a bizarre ratio as an answer of 9.9999e499 as both numerator and denominator...
I was able to run approx(sum(1/x^2,x,1,1000)), and that worked....result was 1.6439..

....with 5000, I get undef in home mode too...