Question

Is TN=2n+n,then find sn

Answer 1

Three concerns:
1. What is TN?
do you mean term(n) ? The general term(n) ?
2. Likewise, what is sn?
are you talking about sum(n), the sum of n terms?
3. If term(n) = 2n + n, why not just say: term(n) = 3n

Fix those and I will look at your question.

Answer 2

The only way I can see to make sense of "2n+n" is to read it as 2^n + n
In that case, recall that

n
∑ 2^n = 2^(n+1) - 1
k=1
since it's just a geometric series

and

n
∑ k = n(n+1)/2
k=1