8689

This number is a prime.

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8689 has two properties related to semiprimes: (1) 8689 is the smaller member of a pair of cousin primes (p and p+4) whose average is a semiprime, since the average of cousin primes 8689 and 8693 is 8691 = 3 x 2897. (2) If you turn 8689 upside down it becomes a semiprime, since 6898 = 2 x 3449. 8689 is only the second prime having both of these properties, preceded by 1009 (cousin average = 1011 = 3 x 337, upside down is 6001 = 17 x 353). [Keith]