Increasing Sum of Binomial Coefficients

Theorem
Let $n \in \Z$ be an integer.

Then:
 * $\ds \sum_{j \mathop = 0}^n j \binom n j = n 2^{n - 1}$

where $\dbinom n k$ denotes a binomial coefficient.

That is:
 * $1 \dbinom n 1 + 2 \dbinom n 2 + 3 \dbinom n 3 + \dotsb + n \dbinom n n = n 2^{n - 1}$