Owlet puzzle #57
Released Monday, August 31, 2026 UTC
28
the answer for puzzle #57
The five clues
- A two-digit triangular number.
- Its digit sum is 10.
- It has exactly six divisors.
- A perfect number — its proper divisors sum to itself.
- The second perfect number after 6; also T₇ and 2²·(2³−1) via Euclid's formula with Mersenne prime 7.
Backstory
The second perfect number, following 6: 1+2+4+7+14 = 28. Also the 7th triangular T_7, and equal to 2² · (2³ − 1) — Euclid's formula using Mersenne prime 7. Whether any odd perfect number exists is still open.
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