Owlet puzzle #106
Released Monday, October 19, 2026 UTC
55
the answer for puzzle #106
The five clues
- A two-digit palindromic number.
- A Fibonacci number.
- A triangular number: 1+2+…+10.
- The product 5 × 11.
- Both F₁₀ and T₁₀ — Fibonacci and triangular.
Backstory
55 = F₁₀ = T₁₀ = 5 · 11 is both Fibonacci and triangular — one of only four positive integers with this property, alongside 1, 3, and 21 (proved by Ming Luo in 1989). It's also the tenth Fibonacci number and the tenth triangular number simultaneously.
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