#[Japt](https://github.com/ETHproductions/japt), <s>12</s> 11 bytes

Will need to come back to this later, to see if it can be golfed further.

    ÆVõ+XÃÕc ¯V

[Try it](https://petershaggynoble.github.io/Japt-Interpreter/?v=1.4.6&code=xlb1K1jD1WMgr1Y&input=MywxMw)

    ÆVõ+XÃÕc ¯V     :Implicit input of integers U=n and V=x
    Æ               :Map each X in the range [0,U)
     Võ             :  Range [1,V]
       +X           :  Add X to each
         Ã          :End map
          Õ         :Transpose
           c        :Flatten
             ¯V     :Slice to the Vth element