CEMC Banner

Problem of the Week
Problem E
Four More

For each positive integer \(n\), \(\text{LCM}(1,2,\ldots,n)\) is the least common multiple of \(1, 2, \ldots, n.\) That is, the smallest positive integer divisible by each of \(1, 2, \ldots, n.\)

Determine all positive integers \(n\), with \(1\leq n \leq 100\) such that \[\text{LCM}(1, 2, \ldots, n) = \text{LCM}(1, 2, \ldots, n+4)\]

Note: In solving this problem, it might be helpful to know that we can calculate the LCM of a set of positive integers by

For example, \(\text{LCM}(1, 2, 3, 4, 5, 6, 7, 8) = 2^3\cdot 3^1 \cdot 5^1 \cdot 7^1 = 840\), since the prime factorizations of \(2\), \(3\), \(4\), \(5\), \(6\), \(7\), and \(8\) are \(2\), \(3\), \(2^2\), \(5\), \(2\cdot 3\), \(7\), and \(2^3\), respectively.