27-x-125-216=0

64

1. Recognize that each of the numbers on the list is a cube.

2. Recognize that they are, successively, cubes of 1, 2, 3, ?, 5, 6

3. Speculate that the missing number is the cube of 4, which is 64.

2. Recognize that they are, successively, cubes of 1, 2, 3, ?, 5, 6

3. Speculate that the missing number is the cube of 4, which is 64.

1, 2, 6, 42, 1806, ?????