What's your favorite number and why?

[Nervous Rex]

687-5309........

*867-5309

 

[Nervous Rex]

1729 as it is the smallest number that can be expressed as a sum of two cubes, in two different ways !

That's one of my favorites, because I had a math professor who liked to start class with a story about a mathematician. He started to tell the story of Hardy's taxi cab number, and when he got to the number, he paused and asked the class, "Do you know what that number was?"

And, less than one week earlier, I had read that story in a book, and worked out how 1729 is 9^3 + 10^3 and also 1^3 + 12^3. So, when the teacher asked, I rolled my eyes up like I was calculating, and said "I think it's 1,729."

The teacher said, "That's right!" and he went on to show how the cubes add up. I glanced sideways for a split second, and saw everyone in the first two rows staring at me with their mouths open.

I put my head down and tried to look bored. I thought to myself, "Keep a straight face. They all think you're smarter than you really are - don't ruin it."

 

[Nervous Rex]

One of my favorites is 0.142857 or 1/7, because once you memorize that, you can do fast division by 7.

1/7 = 0.142857 142857 142857 ...
2/7 = 0.2857 142857 142857 ... The same sequence, but you start at the 2.
3/7 = 0.42857 142857 142857 ... The same sequence, but you start at the 4.
4/7 = 0.57 142857 142857 ... The same sequence, but you start at the 5.
5/7 = 0.7 142857 142857 ... The same sequence, but you start at the 7.
6/7 = 0.857 142857 142857 ... The same sequence, but you start at the 8.

For a talent show one time, I did math tricks. For one, I would ask someone for a 3-digit number. I would do the integer division in my head (basic long division), and when I got to the remainder, I would use this trick to add 6 decimal places at the end. Being able to take, say 653, and say 653/7 = 93.285714 in a few seconds looks pretty impressive.