Limiting density of the Fibonacci sequence modulo powers of a prime

Abstract

For a given prime $p$, we determine the limit, as $\lambda \to \infty$, of the density of residues modulo $p^\lambda$ attained by the Fibonacci sequence. In particular, we show that this limiting density is related to zeros in the sequence of Lucas numbers modulo $p$. The proof uses a piecewise interpolation of the Fibonacci sequence to the $p$-adic numbers and a characterization of Wall-Sun-Sun primes $p$ in terms of the $p$-adic absolute value of a number related to the $p$-adic golden ratio.