I’m not sure exactly when strange theories started to circulate about the “number of the beast” in the Book of Revelation, but for the last few centuries, at least, people have taken great delight in making it stretch to all sorts of people, from Napoleon to Hitler to the Pope and so on.
And Tolstoy is having his own little joke with the idea here by having Pierre calculate his own name (by varying the spelling and finally settling on a grammatically incorrect phrase to make it all work).
But I think this chapter captures some of the madness that must have been in the air in 1812. Pierre is no longer thinking about deep philosophical questions. He has only the two things on his mind, Natasha and the impending “showdown” that he believes must come between him and Napoleon. If you multiply this kind of madness out by the rest of the population of Moscow, it must have been crazy days indeed . . .