nCr, nPr and factorials. Choose r items from a set of n, ordered or unordered.
nCr (combinations) counts how many ways to choose r items from n when order does not matter (like lottery numbers). nPr (permutations) counts ordered selections, where arrangement matters (like ranking finishers).
For a 6-from-49 lottery, nCr(49,6) gives the number of possible tickets (just under 14 million), so the chance of one ticket winning is 1 in that number.
Very large values are shown in scientific notation. Factorials grow fast, so n! beyond about 18 is displayed in exponential form.