4x4x4 Rubik's Cube

The 4x4x4 Rubik's Cube is also known as the "Rubik's Revenge" and the "Master Cube".

Invention and the Creator
It was released in 1981. Invented by Péter Sebestény, the Rubik's Revenge was nearly called the "Sebestény Cube" until a somewhat last-minute decision changed the puzzle's name to attract fans of the original Rubik's Cube. Unlike the original puzzle and the 5×5×5 cube, it has no fixed facets: the center facets (four per face) are free to move to different positions.

Facts
The 4x4x4 Rubik's Cube has 7,401,196,841,564,901,869,874,093,974,498,574,336,000,000,000 or about 7.4 quattourdecillion possible combinations.

There are 56 pieces on this cube: 8 corner pieces, 24 edge pieces, and 24 center pieces.

The 4x4x4 Rubik's Cube has a total of 96 stickers.

The current world record for a 4x4x4 Rubik's Cube solve record is 21.54 seconds by Feliks Zemdegs.

How To Solve
There are several methods that can be used to solve a Rubik's Revenge. The most common is "reduction method" because it effectively reduces the 4×4×4 to a 3×3×3. Cubers first group the centerpieces of common colors together, then pair edges that show the same two colors. Once this is done, turning only the outer layers of the cube allows it to be solved like a 3×3×3 cube. However, certain positions that cannot be solved on a standard 3×3×3 cube may be reached. There are two possible problems not found on the 3×3×3. The first is two edge pieces reversed on one edge, resulting in the colors for that edge not matching the rest of the cubies on either face. The second is two edge pairs being swapped with each other, maybe two corners swapped instead depending on the situation and/or method. Situations like these are known as parity errors. These positions are still solvable; however, special algorithms must be applied to fix the errors. Some methods are designed to avoid the parity errors described above. For instance, solving the corners and edges first and the centers last would avoid such parity errors. Once the rest of the cube is solved, any permutation of the centerpieces can be solved. Direct solving of a 4×4×4 is uncommon but possible.