I have a problem which boils down to an extension of the Birthday Problem. If the probability $\bar{p}$ of 2 out of $n$ people having a bithday within $1$ day of each other in $k$ days is:
$ \bar{p}(k;n)=\frac{n!\binom{k}{n}}{k^{n}} $
What is the probability that 2 birthdays occur within $m$ days?
My intuition tells me it is along the lines of:
$ \bar{p}(k;n,m)=1\times(1-\frac{1}{k-m+1})\times(1-\frac{2}{k-m+1})\times\cdots\times(1-\frac{n-m}{k-m+1}) $
but my math background is weak enough for me to severely doubt myself.