555

Do you mean one of these? Tell me which you want and I’ll go deeper.

• As a number (555 in math)

  • Prime factorization: 555 = 3 × 5 × 37
  • Divisibility: divisible by 3 (sum of digits 15), by 5 (ends with 5), by 15
  • Other facts: 555 = 5 × 111, 555 is odd, 555 ≡ 6 (mod 9)
  • Roman numerals: 555 = DLV

• 555 timer IC (electronics)

  • Pinout (8-pin): 1 GND, 2 TRIG, 3 OUT, 4 RESET, 5 CTRL, 6 THRS, 7 DISCH, 8 VCC
  • Modes:
    • Astable: generates a continuous square wave
      • f ≈ 1.44 / ((R1 + 2R2) C)
      • Duty cycle ≈ (R1 + R2) / (R1 + 2R2)
    • Monostable: produces a single pulse when triggered
      • Pulse width t ≈ 1.1 × R × C (with appropriate R and C)
  • Common use: timers, oscillators, pulse-width modulation, debouncing, etc.

• 555 in Roman numerals

  • 555 = DLV

If you specify which one you’re after (or share the exact exam context), I’ll tailor a concise, exam-ready summary or worked examples.