# Summing polynomials [closed]

I have a ´Univariate Polynomial Ring in t over Symbolic Ring´

```
sage: cj_t = (-1)**(j-1)/factorial(j-1)*(-j+a)**(j-1/2)*exp(-j)*(t+j)**(-1)
```

How can I compute the sum over j from 1 to N?

```
sage: sum(cj_t,1,N)
```

doesn't work.

```
sage: sum([cj_t for j in [1..N]])
```

(Python syntax) doesn't work either.