Owlet puzzle #115
Released Wednesday, October 28, 2026 UTC
225
the answer for puzzle #115
The five clues
- A three-digit multiple of forty-five.
- A three-digit odd perfect square.
- The square of a triangular number.
- The square of fifteen.
- By Nicomachus, the sum of the first five cubes: 1³+2³+3³+4³+5³.
Backstory
225 = 15² = T₁₄ + T₁₅ = 105 + 120 by the identity T_n + T_{n+1} = (n+1)². It's also expressible as 12² + 9² = 144 + 81, since its factorization 3²·5² inherits the sum-of-two-squares property from 5 = 2² + 1².
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