Having trouble understanding O-notation. This is the question:

10. The approximate number of iterations of an algorithm with data size N is determined to be: 1 + 2 + 3 + ... + N

a. Write a table that shows N and the number of iterations for the first 10 values of N.

b. What is the O-notation for this algorithm?

I think the O-notation is O(N) but I am not sure. Any help would be appreciated. Thanks.