Introduced by Michael Keith
in 1987, Keith Numbers
(also known as repfigit numbers
from repetitive Fibonacci-like digit
) can be described:
A Keith Number is a n digit integer N with the following property: If a Fibonacci-like sequence (in which each term in the sequence is the sum of the previous n terms) is formed, with the first n terms being the decimal digits of the number N, then N itself occurs as a term in the sequence.
The On-Line Encyclopedia
of Integer Sequences
gives 197 as an example:
1, 9, 7, 17, 33, 57, 107, 197, ...
According to Michael Keith, there are only 71 Keith Numbers less than 1019.