209

This number is a composite.

+ The curve 42x2 - y2 = 209 contains the 'prime points' (3, 13), (5, 29), (7, 43), and (13, 83). [Buddenhagen]

+ 209 = 11 x 19 is a member of a series n(n + 1) - 1 with the property that all terms greater than 1 are divisible by primes of form 10k + 1 or 10k - 1, but not 10k + 3 or 10k - 3. There is an infinity of pairs x,y where x2 - y2 - xy = 209 for x, y integer. [McNamara]

+ The smallest composite primorial - 1.

+ The number of consecutive composite numbers that follow the prime 20831323, the first prime gap exceeding 200.

+ 209^0 + 209^1 + 209^2 is a prime number. [Raghava]

(There is one curio for this number that has not yet been approved by an editor.)

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