#[Japt](https://github.com/ETHproductions/japt), 7 bytes

 óV äe e

[Try it](https://petershaggynoble.github.io/Japt-Interpreter/?v=1.4.6&code=81Yg5GUgZQ&input=WydhJywnYScsJ2EnLCdiJywnYicsJ2InXQoz)

 óV äe e U = char array, V = n
 óV Split into an array that contains every Vth element of the input
 äe Check if each pair is equal
 e Check if all are true