Can someone tell me how 9/11/2001 adds up to 23? According to the movie, "The Number 23" it does.?

Question

9/11/2001 - if you add 9+11 then you have to follow suite and add 2003, which equals 2021. They are adding 9+11 as whole numbers but then saying that 2001 isnt a whole number and that the zeros some how disappear. But even if that is the case that still equals 21 which would make it 41 all together. If you only add the 2 and the 1 in 2001 then you have to assume that you have to seperate the 1's in 11. Therefor it will equal 14. I do not see anyway to add these numbers to 23 without it being mathematically impossible. Can you?

Answer 1

um.. i am not good at math so i don't know !

Answer 2

21+11-9