Owlet puzzle #64
Released Monday, September 7, 2026 UTC
4181
the answer for puzzle #64
The five clues
- A four-digit Fibonacci number.
- A composite Fibonacci in the four-digit range.
- A four-digit composite Fibonacci at a prime index — an unusual case.
- Not prime: it factors as 37 × 113 — a rare non-prime Fibonacci with prime index.
- The smallest Fibonacci pseudoprime — passes some primality tests despite being composite.
Backstory
4181 = F₁₉ = 37 · 113. It's the smallest composite Fibonacci number whose index is prime, and it acts as a Fibonacci pseudoprime — passing certain Fibonacci-based primality tests despite being composite. Both 37 and 113 first divide the Fibonacci sequence at index 19.
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