555

Do you want a specific treatment of the number 555? Here are a few quick angles you might find useful for exams. Tell me which you want and I’ll go deeper.

• Arithmetic facts

  • Prime factorization: 555 = 3 × 5 × 37
  • Number of divisors: 8
  • Sum of digits: 5 + 5 + 5 = 15; digital root: 1 + 5 = 6
  • Euler’s totient: φ(555) = 288

• Representations

  • Roman numerals: DLV
  • Binary: 1000101011
  • Hexadecimal: 0x22B

• Contexts

  • Commonly used as a fictional phone number prefix (555) in media
  • 555 timer IC is a classic electronics component for oscillators

If you want, I can turn any of these into a quick practice question (e.g., prove φ(555) = 288, or convert 555 to base 3, etc.). What would you prefer?