# Not recognizing infinite sum as zeta function?

Hi,

Is there a reason why Sage can recognize an infinite series as the zeta function for integers but not fractions (rationals)? For example:

```
sum(1/t^(2), t, 1, oo), sum(1/t^(3), t, 1, oo), sum(1/t^(11), t, 1, oo)
```

returns `(1/6*pi^2, zeta(3), zeta(11))`

But, this:

```
sum(1/t^(3/2), t, 1, oo), sum(1/t^(5.2), t, 1, oo)
```

returns just `(sum(t^(-3/2), t, 1, +Infinity), sum(t^(-5.2), t, 1, +Infinity))`