The number of nondecreasing lists 
consisting of 
elements 
is given by the binomial coefficient
 |
For example, there are six nondecreasing lists of length 2 for elements chosen from 1 to 3: (1, 1), (1, 2), (1, 3), (2, 2), (2, 3), and (3,3).
Ordered List
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Cite this as:
Weisstein, Eric W. "Ordered List." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/OrderedList.html