Summary

You can play a game using the numbers on a car license plate. This was something first done by the Indian mathematical genius Srinivasa Ramanujan.

When he fell ill and was admitted to the hospital, the British mathematician G. H. Hardy, who had worked with him, mentioned that the number on the taxi he had taken was an unremarkable 1729. In response, Ramanujan immediately remarked that 1729 is actually a special number—the smallest number that can be expressed as the sum of two cubes in two different ways, as follows:

1729 = 1³ + 12³ = 9³ + 10³

Even if you don’t have such mathematical genius, you can still play with numbers. You can still enjoy a simpler game that anyone who knows basic addition can play: divisibility evaluation.

The rules used in this game are discussed further in the Notions section of this post.

Implication

There are rules for evaluating whether a given number is a multiple of some other number, and you can play a game using that.

Underlying context – Background behind

No significant background knowledge needed

Notions – Key ideas

• Multiple: A number of which is another number multiplied by an integer
• Divisibility rules
  • Divisible by 2: The last digit is one of 2, 4, 6, 8, or 0.
  • Divisible by 3: The sum of the digits is a multiple of 3.
  • Divisible by 4: The last two digits form a number that is either 00 or a multiple of 4.
  • Divisible by 5: The last digit is 0 or 5.
  • Divisible by 6: The number is both even and a multiple of 3.
  • Divisible by 7: For a four-digit number abcd, if 𝑎 𝑏 𝑐 − 2 × 𝑑 abc−2×d is a multiple of 7, then the number is divisible by 7.
  • Divisible by 8: The last three digits form a number that is either 000 or a multiple of 8.
  • Divisible by 9: The sum of the digits is a multiple of 9.
  • Divisible by 10: The last digit is 0.
  • Divisible by 11: The difference between the sum of the digits in odd positions and the sum of the digits in even positions is either 0 or a multiple of 11.

Index – Source(s)

How to Think Like Mathematicians / 피타고라스 생각 수업
10 Inspired By the Number Plate | Multiples / 자동차 번호판을 보고 하는 상상 | 배수

Trajectory – Where I’m headed now

Sometimes, when I’m bored walking down the street, I’ll play the divisibility evaluation game using the divisibility rules.