Keith number

Summary

In recreational mathematics, a Keith number or repfigit number (short for repetitive Fibonacci-like digit) is a natural number $n$ in a given number base $b$ with $k$ digits such that when a sequence is created such that the first $k$ terms are the $k$ digits of $n$ and each subsequent term is the sum of the previous $k$ terms, $n$ is part of the sequence. Keith numbers were introduced by Mike Keith in 1987. They are computationally very challenging to find, with only about 125 known.