Owlet puzzle #83
Released Saturday, September 26, 2026 UTC
9
the answer for puzzle #83
The five clues
- A one-digit perfect square.
- The largest one-digit composite.
- Odd, and equal to the sum of three consecutive integers: 2 + 3 + 4.
- The largest single-digit odd square, and also 3² = 9.
- The base of the casting-out-nines check used in arithmetic.
Backstory
The largest single digit and 3² = 9. Cast-out-nines works because 10 ≡ 1 (mod 9), so digit sums preserve residues mod 9 — the basis of both the divisibility rule for 9 and much of quick-check arithmetic.
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