I would like to compute $\sum_{k=0}^\infty (1+(-1)^k) x^k$. In Mathematica, one can do
In[1]:= Sum[(1+(-1)^k)*x^k,{k,0,Infinity}]
-2
Out[1]= -------
2
-1 + x
How does it work in Sage? I tried
sage: var('k')
k
sage: sum((1+(-1)^k)*x^k, k, 0, oo)
sum(((-1)^k + 1)*x^k, k, 0, +Infinity)
which doesn't give me any new information.
