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**Thought for the day**: This *Creative Math Prompt* pretty clearly suggests a specific problem: to find the pattern and continue it—but always be prepared for the unexpected!

**Concepts**: prime numbers; exponents and their properties; prime factorizations; analyzing and extending patterns

**Examples of noticing and wondering**

*i notice *that each whole number from 1 through 15 has another number paired with it (let's call it a *code* number), but 0 does not.*I notice *that all of the code numbers have only the digits 0 , 1, 2, and 3.*I notice *that the powers of 2 (1, 2, 4, and 8) have "codes" of 0, 1, 2, and 3 respectively.*I notice *that the codes of prime numbers are powers of ten.*I notice *that when you double a number, you add 1 to its code.

*I wonder* what happens if a triple a code number.*I wonder *if any code numbers contain a digit greater than 3.*I wonder *if the code is related to a different number base.*I wonder *why 0 doesn't have a code number.*I wonder *if the code for 16 is 4 (extending the pattern for powers of 2 above).*I wonder *if there are patterns for powers of 3.*I wonder *how to find code numbers for composite numbers that are not powers of a number.

**Notes**

You can find a more structured activity built around this image in in *Exploration 10: Mathematical Mystery Code* from my book, *Advanced Common Core Math Explorations: Factors and Multiples.*

This code in this image can be exasperating at first, because it is full of many "almost" patterns that begin and then fall apart! There are many ways to think about it. In the end, problem-solvers usually arrive the following:

- Prime numbers are powers of 10 in the code. As the prime numbers increase, the powers of ten increase.
- To find the code number of a composite number, add the code numbers of its factors.

Part of the magic of the code is that you may factor the number in any way you like. For example, to find the code for 24:

24 = 2 • 12 1 + 12 = 13

24 = 3 • 8 10 + 3 = 13

24 = 4 • 6 2 + 11 = 13

24 = 2 • 2 • 2 • 3 1 + 1 +1 + 10 = 13

The code number is 13 no matter how you factor it!

What's going on here? Actually, the code is a different way of showing a number's *prime factorization* (PF)*. *The rightmost digit shows the number of 2s in the PF. The second-from- the-rightmost digit shows the number of 3s in the PF. The next digit to the left shows the number of 5s in the PF, etc. It's a PF place value code!

Algebra students can explore some of the ways in which the code illustrates properties of exponents. There are many additional questions to explore as well:

- Can you explain clearly why the rule "factor the number and add the codes" always works (and always gives the same answer no matter how you factor the number)?
- What happens to the code numbers when you divide? Why? (Does this suggest ideas for writing fractions in code?)
- Find the code number for 1024. What problem do you see? Can you think of a way to fix it? What is the next number that will have this problem?
- Why can't you use the code to represent the number 0?
- How might you use the code to represent fractions?
- How might you use the code to represent radicals such as the square root of 2 or the cube root of 6?
- Is it possible to represent all irrational numbers with the code?

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