What is the next number in the following series: 17 15 14 13 13 14 17 23 ?

Take second order differences like this:

17   -2   +1


15   -1    0


14   -1   +1


13    0   +1


13   +1   +2


14   +3   +3


17   +6


23

The last column looks like the Fibonacci sequence, but starting with 1 and 0 instead of 0 and 1. If we place +5 at the end of the third column, then at the end of the second column we should place a +11, and in the first column we'd get 34.

Posted by e.g. on 2005-02-21 14:10:34