Keith number

Given a base $b$ integer

$$n=\sum _{i=1}^k{d}_i{b}^{i-1}$$

where $d_1$ is the least significant digit and $d_k$ is the most significant, construct the sequence $a_1=d_k,\mathrm{\dots }{a}_k=d_1$, and for $m>k$,

$$a_m=\sum _{i=1}^k{a}_{m-i}.$$

If there is an $x$ such that $a_x=n$, then $n$ is a Keith number or repfigit number.

In base 10, the first few Keith numbers below ten thousand are: 14, 19, 28, 47, 61, 75, 197, 742, 1104, 1537, 2208, 2580, 3684, 4788, 7385, 7647, 7909 (see A007629 in Sloane’s OEIS for a longer listing). 47 is a base 10 Keith number because it is contained the Fibonacci-like recurrence started from its base 10 digits: 4, 7, 11, 18, 29, 47, etc.

Title	Keith number
Canonical name	KeithNumber
Date of creation	2013-03-22 16:00:20
Last modified on	2013-03-22 16:00:20
Owner	PrimeFan (13766)
Last modified by	PrimeFan (13766)
Numerical id	5
Author	PrimeFan (13766)
Entry type	Definition
Classification	msc 11A63
Synonym	repfigit number