![]() Is it divisible by 3? In fact, if you're clever, you might be able to give the answer before summing the digits. ![]() You can do this even for huge numbers that your calculator could never cope with.įor example, try: 111,222,333,444,555,666,777, 888,987. You don't need to do the long division in order to find this out. You can discover whether a number is a multiple of 3 just by checking whether this is true for the sum of its digits.įor example, 12,894 has 1 + 2 + 8 + 9 + 4 = 24 = 3 x 8, so 12,894 is a multiple of 3. Subtract the smaller (27) from the larger (72): 45. Take the result, reverse the digits, and add that number to the one you got when you subtracted. Subtract the smaller number from the larger one. Write down any two different numbers from 1 to 9. Subtract it from the original number you thought of. Finally take away your original secret number. However, no one has been able to prove that this has to happen every time. These sequences are called the "hailstone numbers" because, like hailstones, they go up and down a number of times before inevitably falling to Earth. It seems no matter what number you start with you eventually hit a 1. Start with any number - if it is even divide it by 2, if odd multiply by 3 and add 1 then keep going, writing down the sequence of numbers that you generate. There are many simple questions about numbers that no one has been able to answer. Here Peter M Higgins, author and numbers man, reveals the magic behind something many of us struggle to get our heads around. However, in the numbers world, size doesn't matter when it comes to the fascinating and bizarre. You might not have to be a maths genius to know that a prime is a number greater than 1, which can only be divided by itself and 1, like 2, 3, 5, 7, 11, but to find one that big, GCSE maths would be a good start. A maths wizard has discovered the largest known prime number and it's an amazing 17 MILLION digits long.Ĭurtis Cooper, of the University of Central Missouri, in the US found it by using hundreds of computers networked together.
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