How to do combinations?

[CREinstein]

I am doing combinations math with the formula

R! / N! (R-N)!

I do not seem able to make this formula work in Open Office. Can someone help me? I'm trying to use the formula to do 15,000 calculations based upon another data source but doing them individually would suck..

[GeoffW283]

I'm not sure about open office, but in Excel factorials are implemented with the fact() function, so a combinations formula would look something like:
=FACT(10)/(FACT(3)*FACT(10-3))

[MrShorty]

Exactly what formula are you trying? What are the values for R and N? Something like =FACT(R)/FACT(N)/FACT(R-N) should work -- unless R or N are large enough to cause an overflow error (#NUM).