555

Do you mean 555 in math, Roman numerals, or the 555 timer IC in electronics? Here are quick notes for each so you can pick one:

• Math (number 555)

  • Factors: 555 = 3 × 5 × 37
  • Divisible by 3 and 5 (and 15): 555 = 15 × 37
  • In binary: 555 = 1000101011
  • In hex: 0x22B
  • Quick problem idea: find all divisors or compute 555 mod n for various n.

• Roman numerals

  • 555 = DLV

• Electronics (555 timer IC)

  • Modes: astable, monostable
  • Astable frequency: f ≈ 1 / [0.693 × (R1 + 2R2) × C]
  • Astable duty cycle: D = (R1 + R2) / (R1 + 2R2)
  • Monostable pulse width: t = 1.1 × R × C
  • Useful quick practice: plug in sample R1, R2, C values and compute f and D (or t for monostable).

Tell me which context you want, and I can go deeper or generate practice problems.