Copyright © University of Cambridge. All rights reserved.

'Little Goldbach' printed from https://nrich.maths.org/

Show menu

Both 4 and 8 can be written as the sum of two prime numbers ($4=2+2$, $8=5+3$). How many numbers less than 20 cannot be written as the sum of two prime numbers?

 

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

 

This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.