Owlet puzzle #5
Released Friday, July 10, 2026 UTC
561
the answer for puzzle #5
The five clues
- A three-digit odd number.
- It is not prime, yet passes Fermat's compositeness test for every base coprime to it.
- It is a squarefree product of three primes.
- 561 = 3 · 11 · 17.
- The smallest Carmichael number.
Backstory
First Carmichael number. Alford, Granville, and Pomerance proved infinitely many exist (1994).
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