This is a piece of my second puzzle; it is made of 17 unit cubes. Toghether with 7 other pieces, they fit into a 5x5x5 cube. The solution is unique and so is the order of assembly (see below).

Each piece is formed by a different number of unit cubes, ranging from 12 to 19.
(Do you see what is wrong with that statement?)

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Can you solve this?:



(Unknown author)

This 3x3x3 cube puzzle is "serially interlocking". That is, it can be assembled in one order only.
Open problem: Is there a 3x3x3 serially interlocking puzzle with 5 pieces?

For a different kind of puzzles, try this practice test before registering to compete in the Qualifying Test to represent the USA in the World Puzzle Championship.