Looking back represents the number "9". Because 9 is like a person, leaning forward and leaning back means that the big numbers 7, 8 and 9 must have gone out and don't want to go, and the small numbers 1, 2 and 3 want to look forward and stride forward is the goal, so only 9 is like a top-heavy person, with his head slightly lowered in meditation.

The blue sky represents the number "5", because blue ranks fifth among the seven colors of light.