Extremal orders of the Zeckendorf sum of digits of powers

Abstract

Denote by s_F(n) the minimal number of Fibonacci numbers needed to write n as a sum of Fibonacci numbers. We obtain the extremal minimal and maximal orders of magnitude of s_F(n^h)/s_F(n) for any h>= 2. We use this to show that for all $>N_0(h) there is an n such that n is the sum of N Fibonacci numbers and n^h is the sum of at most 130 h^2 Fibonacci numbers. Moreover, we give upper and lower bounds on the number of n's with small and large values of s_F(n^h)/s_F(n). This extends a problem of Stolarsky to the Zeckendorf representation of powers, and it is in line with the classical investigation of finding perfect powers among the Fibonacci numbers and their finite sums.