  A Keith number is a positive integer N with the decimal representation
a_1a_2...a_n such that n>=2 and N appears in the sequence (K_m) given by the
recurrence K_1=a_1,...,K_n=a_n and K_m=K_{m-1}+K_{m-2}+...+K_{m-n} for m>n. We
prove that there are only finitely many Keith numbers using only one decimal
digit (i.e., a_1=a_2=...=a_n), and that the set of Keith numbers is of
asymptotic density zero.
