how many floors does this building have?
the numbers go up to 31.. and a quick estimate of 3x10 rows.. well, that's close enough.
but wait.. there are 3 basements. ok... check through them all... what's missing?
4, 14 and 24!
sì = 四 = four
sǐ = 死 = death
and, of course, don't forget unlucky 13.