J, ¹³ 12 bytes

[$[:,1++/&i.

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J, ¹³ 12 bytes

[$[:,1++/&i.

Try it online!

how

We take x as the left arg, n as the right. Let's take x = 8 and n = 3 for this example:

• +/&i.: Transform both args by creating integer ranges i., that is, the left arg becomes 0 1 2 3 4 5 6 7 and the right arg becomes 0 1 2. Now we create an "addition table +/ from those two:

     0 1 2
     1 2 3
     2 3 4
     3 4 5
     4 5 6
     5 6 7
     6 7 8
     7 8 9
  

• 1 +: Add 1 to every element of this table:

     1 2  3
     2 3  4
     3 4  5
     4 5  6
     5 6  7
     6 7  8
     7 8  9
     8 9 10
  

• [: ,: Flatten it ,:

     1 2 3 2 3 4 3 4 5 4 5 6 5 6 7 6 7 8 7 8 9 8 9 10
  

• [ $: Shape it $ so it has the same number of elements as the original, untransformed left arg [, ie, x:

     1 2 3 2 3 4 3 4 
  

J, 13 bytes

[{.[:,1++/&i.

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J, ¹³ 12 bytes

[$[:,1++/&i.

Try it online!