172

This number is a composite.

+ 172 is the only byte whose binary representation contains a 1 at bit n iff n is prime (17210 = 101011002). [Thoms]

+ Seventeen 2's followed by two 17's is prime. [De Geest]

+ 172 = π(1+7+2) * prime(1*7*2). It is the only known number (up to 10^8) with this property. [Firoozbakht]

+ 172 = phi(1+7+2) * prime(1*7*2). It is the only known number (up to 10^8) with this property. [Firoozbakht]

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

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