MathDB
Putnam 2018 A4

Source:

December 2, 2018
PutnamPutnam 2018

Problem Statement

Let mm and nn be positive integers with gcd(m,n)=1\gcd(m, n) = 1, and let ak=mknm(k1)na_k = \left\lfloor \frac{mk}{n} \right\rfloor - \left\lfloor \frac{m(k-1)}{n} \right\rfloor for k=1,2,,nk = 1, 2, \dots, n. Suppose that gg and hh are elements in a group GG and that gha1gha2ghan=e,gh^{a_1} gh^{a_2} \cdots gh^{a_n} = e, where ee is the identity element. Show that gh=hggh = hg. (As usual, x\lfloor x \rfloor denotes the greatest integer less than or equal to xx.)