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Counting & ProbabilityChallengeDistributions: Stars & Bars and Integer Solutions

Distributions: Stars & Bars and Integer Solutions · Challenge problem

How many integer sequences 1≤a1≤a2≤⋯≤a61\le a_1\le a_2\le\cdots\le a_6 satisfy ai≤ia_i\le i for every i=1,…,6i=1,\dots,6?