MathCastle
Number TheorySuperchallengeFactors & Multiples

Factors & Multiples · Superchallenge problem

How many subsets of {1,2,3,…,20}\{1, 2, 3, \ldots, 20\} have least common multiple equal to lcm⁡(1,2,…,20)\operatorname{lcm}(1, 2, \ldots, 20)?