Edit - oh, you beat me to it. Well, never mind.
Spoiler for Astronomical numbers and chapels:
It's in the "Possibility of a 19th person" chapter, right after the "Hempel's Raven" silliness.
I somewhat doubt this number being written on the chapel, as it would be "Sixty-four quadrillion three hundred fifty-eight trillion two hundred twenty-three billion five hundred seventy-nine million six hundred seventy-three thousand two hundred four".. which is a tad for an inscription over a door. And I doubt the insctription is in numerals, since I'm assuming even Battler knows how to read those.
That's not to say you couldn't be right; still, where would that leave us?