# how to count elements

by epsi00
Tags: elements
P: 891
 Quote by Norwegian We can perhaps interpret the question as follows: Let u(n) be the cardinality of the set {a*b: a,b in {1,2,...,n}}. For example, u(3)=6 and u(7)=25. Is there some kind of general formula, or a clever way to determine u(n)? In particular, what is u(1000)?
That is right but no formula apparently exists for u(n) but see https://oeis.org/A027424

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