(I'm a programmer, please excuse my abuse of or lack of proper mathematical language)
The other day I needed to find a natural number that is cleanly divisible by all integers in the range [1,10]
To start, I figured I'd just multiple them all:
1 * 2 * 3 * 4 * 5 * 6 * 7 * 8 * 9 * 10 (a.k.a. 10!) = 3628800 3628800 mod 1 = 0 3628800 mod 2 = 0 3628800 mod 3 = 0 3628800 mod 4 = 0 3628800 mod 5 = 0 3628800 mod 6 = 0 3628800 mod 7 = 0 3628800 mod 8 = 0 3628800 mod 9 = 0 3628800 mod 10 = 0 Well, that works, but I thought I could probably find a smaller number. I figured that I could remove e.g. the factor 6, because it can be made by multiplying the factors 2 and 3 that are also in the list.
So I tried just including prime numbers:
1 * 2 * 3 * 5 * 7 * 9 = 1890 1890 mod 1 = 0 1890 mod 2 = 0 1890 mod 3 = 0 1890 mod 4 = 2 uh-oh So, that doesn't work. It's because while 4 can be made by multiplying 2 and 2, there is only one 2 in the list.
What I eventually end up with is:
1 * 2 * 4 * 5 * 7 * 9 = 2520 Or: A set of numbers in a range [1, N] that only includes those numbers that cannot be made by multiplying other numbers in the set, where each of those numbers may be used only once.
Now, the question (which is purely out of curiosity): Is this a common, known, named mathematical concept?