How many domino pieces are in a double-6 set of dominos?

Question

There will be a double-0, double-1, double-2, double-3, double-4, double-5, and double-6.  As you solve the problem, consider the two reversed dominos only once.  For example, the 5-6 domino and the 6-5 domino would only count once.

Answer 1

So, there will be:

0-0

0-1

0-2

0-3

0-4

0-5

0-6

That's 7 dominoes with a 0 on them. Since the 1-0 won't count because it's already been listed, how many dominoes have a 1 on them?

The 2-0 and 2-1 dominoes won't count a second time, so how many dominoes have a 2 on them?

Continue the pattern to find your answer. Let me know what it is, and I'll check it for you.