Why Do Numbers Seem to Multiply in the Dark?

Imagine you're playing with blocks. When you put one block beside another, it feels like there are more of them, kind of like they’re multiplying just by being next to each other. Numbers can do something similar when they are alone, making it feel as though they grow or multiply in the dark.

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Examples

  1. A child sees the number 3 on a dark wall, and suddenly thinks of 6 and then 9.
  2. You're in bed at night and think about 10, soon you imagine 20 and even 40.
  3. A kid sees the number 7 and starts counting by sevens: 7, 14, 21.

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