Many years ago, my high school maths teacher showed me a mysterious number 142857. This number has always remained in my memory since it’s so intriguing.
To follow along, you would probably need a calculator. Unless you are one of those who could do numbers in his head. 
How to memorise this number
Think of the approximation to PI, i.e. 22/7 (that is, 22 divided by 7).
22/7 = 3.142857
You see that the first six decimal numbers of 22/7 is 142857.
Note the actual value of PI to six decimal places is of course:
PI = 3.141593
Not quite equal to 22/7 but close enough for rough high school calculations.
What so special about this number?
If you multiply 142857 by an integer 1 to 6, you get back the same number, but “rotated”:
1 x 142857 = 142857 2 x 142857 = 285714 3 x 142857 = 428571 4 x 142857 = 571428 5 x 142857 = 714285 6 x 142857 = 857142
If you multiply by 7, you get:
7 x 142,857 = 999999
And much more… you can read all about it in the Wikipedia article on 142857.
So what?
Well, this number popped up in my head now and again all these years, so I thought I would share it and put the same curse on you. 
Of course, I didn’t know much about it then, only that you could keep playing multiplications and keep seeing the same pattern. But now, thanks to Wikipedia, I finally know the number is called a cyclic number.
But that’s just too much maths for me; 142857 is more than enough.
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