8647
This number is a prime.
8647 is the only 4-digit prime that is 2 less than a square
(8649 = 93^2) and 1 more than a triangular number (8646 is
the 131st triangular number). [Keith]
James Comey once shared a picture on Instagram of seashells
on a beach arranged into the numbers "8647." The caption
read: "Cool shell formation on my beach walk." [Lewicki]
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