some math for u

tis is for the husband...

* 111,111,111 multiplied by 111,111,111 gives a result of 12,345,678,987,654,321

* Multiply 21978 by 4 and you get 87912, which is the original number in reverse.

* 12345679 multipled by a product of 9 gives a nine digit sequence of the factor used. For example, 12345679 × (1 × 9) = 111111111, 12345679 × (2 × 9) = 222222222, etc. (This only works for single digit multiples of 9.)

* 142857 is known as a cyclic number: the individual digits always appear in different positions when multiplied by any number from 1 to 6. (142857 × 2 = 285714, 142857 × 3 = 428571, 142857 × 4 = 571428, 142857 × 5 = 714285, 142857 × 6 = 857142.)

* Pick any prime number larger than 5, multiply it by itself (i.e, find the square of the prime number you picked), add 17 to it and divide it by 12: you will always get a remainder of 6.


or do you already know these?