MathIsFun.com and StatTrek.com offer free online calculators that figure out combinations. Combinations are sets of numbers or objects that are chosen and placed in no particular order.
On MathIsFun.com, users enter how many types of objects there are to choose from, how many will be chosen and whether repetition is allowed. Once submitted, the site generates a the requested combinations.
The StatTrek.com calculator asks users to enter the number of sample points in the set and the number of sample points in each combination, then calculates the number of combinations possible. The website also explains that statisticians refer to the types of objects listed as "n" and how many objects are in the combination as "r."