Brain Teasers
Dynamic Duo
What two numbers are missing from this series?
2, 3, 5, 7, 11, 13, __, 31, 37, __, 73, 79, 97, ...
Extra challenge: What is the next number in the series?
2, 3, 5, 7, 11, 13, __, 31, 37, __, 73, 79, 97, ...
Extra challenge: What is the next number in the series?
Hint
Primary question: The two numbers are related to each other.Extra challenge: The next number stands alone.
Answer
The two missing numbers are 17 and 71.Here is a list of prime numbers:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, ...
This series includes only primes whose digit(s), when reversed, also form primes.
The first few primes are their own reverse: 2, 3, 5, 7, and 11. The other primes listed in the series come in pairs: 13 and 31, 17 and 71, 37 and 73, 79 and 97.
The extra challenge is to find 101, which is its own reverse.
Hide Hint Show Hint Hide Answer Show Answer
What Next?
View a Similar Brain Teaser...
If you become a registered user you can vote on this brain teaser, keep track of which ones you have seen, and even make your own.
Solve a Puzzle
Comments hidden to avoid spoilers.
Follow Braingle!