How do I program this?

example:

n = 30

265-(n-1) = 265-(29) = 236

*How do I program the product from 265 down to 265-(n-1)?

265*264*263*262*261*260*.....*240*239*238*237*236 =

It is a factorial calculation but I'm not doing the entire 265!.

Thank-you.

Sounds like you want the permutation operation: 265 nPr 30. This is mathematically equivalent to 265!/(265-30)!.

When working with factorials like that understanding nCr and nPr can come in handy.

nPr here is the exact operation you are looking to do
this case would 265 npr 30 when n=30
265 npr n if trying to generalize what you asked

Quick explanation of commands:
nCr - Combinations. n objects in r positions where order does not matter
ABC BAC CAB etc all count as the same combination
nPr - Permutations. n objects in r positions where order does matter
ABC BAC CAB count as 3 seperate permutations.

What will really help in this case are the formulas for these
nPr = n! / (n-r)!
nCr = n! / ( (n-r)! (r!) )

http://tibasicdev.wikidot.com/npr for npr
http://tibasicdev.wikidot.com/ncr for ncr
Both are found under Math->Probability

as another piece of trivia 265! is the same as 265 nPr 265.

Awesome. That worked. Thank-you!