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Odd Differences

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How Old Am I?

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One Basket or Group Photo

Libby Jared helped to set up NRICH and this is one of her favourite problems. It's a problem suitable for a wide age range and best tackled practically.

Below 400

Stage: 4 Short Challenge Level: Challenge Level:1
See all short problems arranged by curriculum topic in the short problems collection

If the pattern below is continued, what number will appear directly below 400?

      2   3   4    
    5   6   7   8   9  
 10   11   12   13   14   15 
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.