# Easy (beginner) sum problem:"need a summation variable"?

My native language is not english but I try my best to make you understand the problem. I'd like to: from k=1 to n+1 sum k^2

But when I try to solve it with sage, it gives me an error.

(k,n)=var('k,n') show(sum(k,k^2,1,n+1))

It has a problem with k^2. How to solve it?

Many thanks.