555

Do you mean one of these?

• The number 555: quick facts (math, Roman numerals, properties)

  • 555 = 3 × 5 × 37
  • Roman numeral: DLV
  • Divisible by 3 and 5; digits sum to 15

• The 555 timer IC (electronics): quick intro

  • Modes: astable (free-running oscillator) and monostable (one-shot)
  • Key formulas (typical, with diodes omitted):
    • Astable: f ≈ 1 / [0.693 (RA + 2RB) C] T_high ≈ 0.693 (RA + RB) C T_low ≈ 0.693 RB C
    • Monostable: T ≈ 1.1 RC
  • Used for timers, oscillators, PWM, etc.

• The time 5:55

  • If you mean a clock time, that's 5:55 AM/PM.

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