Returns the number of combinations of a subset of items.
- n is the number of items in the set.
- k is the number of items to choose from the set.
- COMBINA returns the number of unique ways to choose these items, where the order of choosing is irrelevant, and repetition of items is allowed. For example if there are 3 items A, B and C in a set, you can choose 2 items in 6 different ways, namely AA, AB, AC, BB, BC and CC; you can choose 3 items in 10 different ways, namely AAA, AAB, AAC, ABB, ABC, ACC, BBB, BBC, BCC, CCC.
- COMBINA implements the formula:
- returns 6.
- returns 10.