### Today’s Puzzle:

Last time I published a puzzle with the last clue missing. Leaving out the first or the last clue only makes the puzzle slightly more difficult. What if I left out a clue more in the middle of the puzzle. I gave that some thought and designed today’s puzzle. I soon realized that I had to let you know that the 12 is one of the last eight boxes. There is only one solution. Can you find it?

I posted a solution video for it on Twitter:

In this video, I show how to solve this puzzle. The method I use works because if a – b = c, then c + b = a,

and if a – b = c, then (a – d) – (b – d) = c, as well. pic.twitter.com/90whxDYnHA— Iva Sallay (@findthefactors) January 21, 2022

### Factors of 1715:

- 1715 is a composite number.
- Prime factorization: 1715 = 5 × 7 × 7 × 7, which can be written 1715 = 5 × 7³.
- 1715 has at least one exponent greater than 1 in its prime factorization so √1715 can be simplified. Taking the factor pair from the factor pair table below with the largest square number factor, we get √1715 = (√49)(√35) = 7√35.
- The exponents in the prime factorization are 1 and 3. Adding one to each exponent and multiplying we get (1 + 1)(3 + 1) = 2 × 4 = 8. Therefore 1715 has exactly 8 factors.
- The factors of 1715 are outlined with their factor pairs in the graphic below.

### More About the number 1715:

1715 = 1·7³·1·5. Thank you, OEIS.org for that fun fact!

1715 is the hypotenuse of a Pythagorean triple:

1029-1372-1715, which is (3-4-**5**) times **343**.

1715 = 5·7³.

5·7º = 2² + 1².

5·7¹ cannot be written as the sum of two squares.

5·7² = 14² + 7².

5·7³ cannot be written as the sum of two squares.

5·7⁴ = 98² + 49².

What do you notice? What do you wonder?