Stepwise Codes
Let’s arrange all 3 digit binary codes in a list starting with 000 such that each code differs from its previous code by only 1 digit.
Subtraction Polygons
Consider the subtraction game that goes like this: Write down one whole number at each corner of the square below, then fill in each side with the positive difference the two neighbouring corners and connect the four new numbers in a smaller square. Repeat the subtraction to continue forming new squares in the middle.
3D Sudoku
Imagine instead of a two dimensional grid, we are now filling a 3D grid made up of nxnxn unit cubes with numbers 1 to n such that every row, column, and depth has exactly one of each number.