Maybe this is a boring question, but I cannot figure it out. Because every expression has a Head, and Head[1] is Integer, and Head[Integer] is Symbol. Therefore, 1 should somehow represented as Symbol["Integer"][1] or something similar. However, Depth[1]=1 which means 1 should be presented as Symbol["Integer..."], not as a expression of depth 2, such as Symbol["Integer"][1].

Therefore, what is correct representation of 1?