The way I think about it is less as an encyclopedia of sequences per se than it is a kind of projection of mathematics onto sequence-space. The point being that an integer sequence, because it often has so many mathematical interpretations, acts in some sense like the intersection of those interpretations. There are of course many ways in which two or more mathematical concepts are linked, but a shared integer sequence is among the most useful, precisely because it can be browsed and searched like an encyclopedia.