Counting the Number of Reps From a Rep Height I'm trying to calculate the number of reps from a rep height.
Example #1
Input: n = 2
Output: Result = 6
Because 1+2+2+1 = 6
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Example #2
Input: n = 3
Output: Result = 12
Because 1+2+3+3+2+1 = 12
What formula could I use to get from input to output?

My way before is unnecessarily long. When you add $(1 + 2 + \dots + n) + (n + (n-1) + \dots + 1)$, line up the pairs $(n, 1)$, $(2, n-1)$, $(3, n-2)$, and you'll notice that they all sum to $n+1$. Since you have $n$ pairs, the sum is $n(n+1)$. 
