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Meet The Creators

  • Educator Steve Wyborney
  • Director Outis
  • Script Editor Alex Gendler


Additional Resources for you to Explore
Prime numbers and divisibility play an important role in this riddle. One of the significant numbers in the riddle has exactly 4 factors – and 2 of those factors are prime numbers.

Another number that fits that description is 35. The factors of 35 are 1, 5, 7, and 35. Notice that the 2 factors in the middle of the sequence of factors (5 and 7) are both prime numbers.

Likewise, the number 15 has 4 factors, which include 1, 3, 5, and 15. Again the 2 factors in the middle of the sequence (3 and 5) are both prime numbers.

Can you identify other numbers which have exactly 4 factors, and in which the middle two numbers in the sequence of factors are both prime?

As an additional exploration, can you identify numbers which have exactly 4 factors, but do not have two prime numbers in the middle of the sequence? Why or why not?

Is it possible that a number could have an odd number of factors, and if so, what would those numbers have in common?

Love riddles involving numbers? Start here with: How many ways can you arrange a deck of cards? and Can you solve the counterfeit coin riddle?

Not the least bit puzzled when solving riddles? TED Ed-has a whole section of riddles! Click here, sit down with your family or friends, and start solving them!