This should be a simple combinatorial problem. Suppose I have a number n which is a positive integer. Suppose, that there are four numbers a,b,c,d such that 0<=a<=b<=c<=d<=n.(adsbygoogle = window.adsbygoogle || []).push({});

The question is how many quadruples of the form (a,b,c,d) can be formed out such arrangement?

I realize that this is a homework-like question, but I am really interested in seeing which principles of combinatoris would apply here.

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# Quadruples of Integers

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