Owlet puzzle #61
Released Friday, September 4, 2026 UTC
89
the answer for puzzle #61
The five clues
- A two-digit number ending in nine.
- It is prime.
- A Fibonacci number.
- The 11th Fibonacci number.
- 1/89 ≈ 0.011235… — its decimal expansion spells out the Fibonacci sequence.
Backstory
89 = F₁₁, and 1/89 = 0.01123595505… encodes the Fibonacci sequence itself: 1/89 = Σ F(n)·10^(−n−1). This works because 89 = 10² − 10 − 1, the characteristic polynomial of Fibonacci evaluated at 10. 89 is also a Sophie Germain prime, since 2·89 + 1 = 179 is prime.
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