Let A \subseteq N

f: N -> [0,\infty], f(n)=a_n

\mu_d(A)=n, A ~has ~n ~elements
\mu_d(A)=+\infty, A ~has ~\infty ~elements

1. Prove that \mu_d is measure on P(N), and f is \mu_d measurable function.

2. Calculate: \int_N f d\mu_d