This number is a composite.

+ 166 is the smallest number such that the number and its reversal are both congruent to 1 mod p for the same set of some three distinct odd primes (166 = 661 = 1 mod (3, 5, 11)). [Thoms]

+ 166!-1 is a factorial minus one prime. [Dobb]

+ The smallest Smith number that is prime when reversed (661), turned upside down (991), and reversed-then-turned upside down (199). You get the next case by inserting a zero between the digits (10606). [Capelle]

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