If an=2an−1+1a_n = 2a_{n-1} + 1an=2an−1+1 with a0=0a_0=0a0=0, what is ana_nan?
2n−12^n - 12n−1
2n+1−12^{n+1} - 12n+1−1
2n2^n2n
2n+12^n + 12n+1