Thanx for answering. Of course p is a factor of p!, but not necessarily of nCr(p,r). To be a factor of nCr(p,r) it has to devide nCr(p,r) exactly, that is division by p will give an integer as an answer. e.g. nCr(11,3) =165 and 11 devides 165 exactly 165/11 = 15. This holds only for primes in the formulae nCr(p,r) not for composites e.g. nCr(6,2) = 15 but 6 does not divide 15 exactly 15/6 =2.5
I understand that r does not devide p. A prime is only divisible (exactly) by 1 and itself, but I don't quite see the relevance of this fact to my question.
nCr(p,r) [/SIZE]are divisible by p. Where does n come from? You said nothing about it anywhere. Now you need to learn to post what you mean.
If that is not the question then why did you post it that way?
Sorry, my notation was a bit sloppy. What I meant by nCr was "n choose r" from combinatorics. Perhaps I should have used the alternative notation , C(p,r), instead. The number of combinations of selecting several things, r, out of a larger group. p.