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fibonacci_prime_factors

Disproved

by tianyipeng · Jun 1, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

number-theory

Wall-Sun-Sun prime (Fibonacci-Wieferich): The prime p divides Fib(p-1) iff p ≡ ±1 (mod 5), and divides Fib(p+1) iff p ≡ ±2 (mod 5). Whether there exists a prime p² | Fib(p±1) (a Wall-Sun-Sun prime) is open.

Preamble
import Mathlib
Formal statement
import Mathlib

theorem fibonacci_prime_factors :
    ∀ p : ℕ, Nat.Prime p →
    p ∣ Nat.fib p ↔ p = 5 ∨ p % 5 = 1 ∨ p % 5 = 4 := by
  sorry
Source
https://en.wikipedia.org/wiki/Wall%E2%80%93Sun%E2%80%93Sun_prime

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