555

Quick question: what would you like to review about 555? Here are common options. Pick one (or tell me another topic):

• Math / number theory

  • 555 = 3 × 5 × 37
  • Divisors: 1, 3, 5, 15, 37, 111, 185, 555
  • Sum of divisors σ(555) = 912
  • Euler’s totient φ(555) = 288
  • Number of divisors τ(555) = 8
  • Roman numerals: 555 = DLV

• Electronics (555 timer IC)

  • Monostable: t ≈ 1.1 · R · C
  • Astable: f ≈ 1.44 / [(R1 + 2R2) · C]
  • Duty cycle, typical pinout, when to use each mode

• Other

  • 555 in Thai texting (555 means laughter)
  • Any other context you had in mind?

If you want, I can give you a quick cheat sheet or a couple of practice questions for your chosen topic.