Scaling an exponential maximum

For independent \mathrm{Exp}(2) variables, give a_n and b_n that produce the Gumbel limit.

For an exponential rate \lambda the centring (\log n)/\lambda and the scale 1/\lambda produce the Gumbel limit. Here \lambda=2, so b_n=(\log n)/2 and a_n=1/2.