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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.