The unusual thing about this number is that the most common phrases that use it are wrong. That is, while someone may often say there are X As in a B, the actual number is not X.
What number am I thinking of?
"There are X As in a B", but almost every B contains at least X + 2 As.
"There are X Cs in a D" but a D always contains between X + 0.1 and X + 0.3 Cs