The next number is 21, because the sequence is the Fibonacci sequence where each number is the sum of the two preceding numbers. For example,1+1=2,1+2=3 2+3=5, and so on, so to find the next number, you add the last two:8+13=21.
Which number should come 1 -1 -2 -3 -5 -8 -13----------?
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