MathDB
2016-2017 Fall OMO Problem 6

Source:

November 16, 2016
Online Math Open

Problem Statement

For a positive integer nn, define n?=1n⋅2n−1⋅3n−2⋯(n−1)2⋅n1n?=1^n\cdot2^{n-1}\cdot3^{n-2}\cdots\left(n-1\right)^2\cdot n^1. Find the positive integer kk for which 7?9?=5?k?7?9?=5?k?.
Proposed by Tristan Shin
Back to ProblemsView on AoPS