C# - Choosing X Elements From Set Of N (Number Combination)

I have 9 numbers 1,2,3,4,5,6,7,8,9. I want different combinations of 5 numbers out of 9 numbers (no repeat of same numbers in a row). E.g. 1,2,3,4,5 - correct, 1,1,2,3,4 - wrong

I want no duplication either
E.g.:
1,2,3,4,5
1,2,3,5,4

Any formula which works for 8 or 9 or 10 or n numbers. I know there is 126 ways C(9,5)=(9!)/(4!.5!)=...=126 ways. I need the code to generate unique set numbers
E.g.:
1,2,3,4,5
1,2,3,4,6
2,3,4,5,6