Introduction
To determine whether an n-digit number N is a Keith number, create a Fibonacci-like sequence that starts with the n decimal digits of N, putting the most significant digit first. Then continue the sequence, where each subsequent term is the sum of the previous n terms. By definition, N is a Keith number if N appears in the sequence thus constructed.
As an example, consider the 3-digit number N = 197. The sequence goes like this:
- 1, 9, 7, 17, 33, 57, 107, 197, 361, ...
Because 197 appears in the sequence, 197 is seen to be indeed a Keith number.
Read more about this topic: Keith Number
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