I guess アキラの国民番号 must be in the form 12345xy6789 - five "upper digits", four "lower digits", and two letters in the middle, and the answer is then something like 1111xy12345, where 1111 is the number you calculated in the first step.
That's a pretty obnoxiously long-winded scheme for getting into the site. Usually it's just "enter birthday of my favourite character!♪☆♫!" or some reasonably obvious reference to some well-known example of 語呂合わせ.