Zero is the most complex number among 0-9. It can be nothing, and can also be something that expands other number. For example, append 0 after 1, it expands 1 to another larger number 10.
Number 1-9 just can be something. They don’t expend other number.
Another interesting fact: (I bet most of us know about the first fact, but maybe not the second one…)
- Any number times 0 goes back to 0 itself.
- Any number times 9 goes back to 9 itself, no exception.
2*9 = 18 (1+8 = 9)
7*9 = 63 (6+3 = 9)
99*9 = 891 (8+9+1 = 18 –> 1+8 = 9)
836*9 = 7524 (7+5+2+4 = 18 –> 1+8 = 9)
2017*9 = 18153 (1+8+1+5+3 = 18 –> 1+8 =
25379*9 = 228411 (2+2+8+4+1+1 = 18 –> 1+8 =9)
After I noticed this interesting fact, I did a search on the Internet.
Why is it that if you multiply any number by nine and add up the digits of the product, they also equal nine? For example 9×12=108. 1+0+8=9
Why is everything multiplied by nine when the digits are added the result is nine? (pdf)
