### Sage Math Cloud Plotting Error, ValueError: cannot convert x to int

I'm using SageMathCloud to compute a summation

```
sum([.25^(100-i) * .75^(i) * binomial(100,i) for i in range(0, 63)])
0.00274614363169321
```

but am not able to plot it

```
plot(sum([.25^(100-i) * .75^(i) * binomial(100,i) for i in range(0, x)]),(x,1,63))
Error in lines 1-1
Traceback (most recent call last):
File "/projects/sage/sage-6.9/local/lib/python2.7/site-packages/smc_sagews/sage_server.py", line 905, in execute
exec compile(block+'\n', '', 'single') in namespace, locals
File "", line 1, in <module>
File "sage/symbolic/expression.pyx", line 1084, in sage.symbolic.expression.Expression.__int__ (/projects/sage/sage-6.9/src/build/cythonized/sage/symbolic/expression.cpp:8329)
raise ValueError("cannot convert %s to int" % self)
ValueError: cannot convert x to int
```

What am I doing wrong here?