A staircase-brick with 3 steps of width 2 is made of 12 unit cubes. Determine all integers for which it is possible to build a cube of side using such bricks.
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A staircase-brick with 3 steps of width 2 is made of 12 unit cubes. Determine all integers $n$ for which it is possible to build a cube of side $n$ using such bricks.
Source: Međunarodna matematička olimpijada, shortlist 2000
Školjka 
for which it is possible to build a cube of side