Prime Curios!: 172

172
(another Prime Pages' Curiosity)

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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 = (1+7+2) * prime(1*7*2). Note that 172 is the only known number (less than 20000000) with this property. [Firoozbakht]