How to list all the combinations from the following:-

From the numbers 1 to 20 there are 4845 4 digit combinations - no repeat numbers.

Using the lottery as an example, how would you list all of the 6 digit combinations (almost 14 million), in order to write them out.
This is for examle only, I would be grateful for the answer re- 4 digits from 20.

Thank you!

So what do YOU think ?

Not sure what you mean by "write them out" - please clarify. You seem to be aware of how to determine what the number or possible combinations are - so are you trying to write a computer program to write them all out, or an excel spreadsheet?