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Leonard writes down a sequence of numbers. After the first two numbers, each number is the sum of the previous two numbers in the sequence. The fourth number is $6$ and the sixth number is $15$. What is the seventh number in the sequence?
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.
Fibonacci Deduction
Age 11 to 14
ShortChallenge Level 
Leonard writes down a sequence of numbers. After the first two numbers, each number is the sum of the previous two numbers in the sequence. The fourth number is $6$ and the sixth number is $15$. What is the seventh number in the sequence?
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.
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