



 
Beth, this is the 'formula' for the Fibonacci numbers but it is not easy to implement: Penny Beth wrote back
Beth, I'm not sure what you're asking. The formula for the Fibonacci numbers is often called the Binet Formula. To use it for n = 20 is not really practical  we would use the formula to estimate the size of large Fibonacci numbers but for small n it is easier to use the recurrence F(n+1) = F(n)+F(n1). The sequence starts off 1,2,2,3,5,8,13, ... . Each successive value is obtained from adding the two previous ones  for example the next number in the sequence is 8+13 = 21. This is the easiest way to get the 20th term. Penny  


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