555

Do you mean the number 555, or the 555 timer IC in electronics? Here are quick notes for both.

If you mean the number 555:

• Prime factorization: 555 = 3 × 5 × 37
• Decimal to other bases: Binary 1000101011; Hex 0x22B; Roman numerals: DLV
• Properties: divisible by 3 and 5 (digits sum is 15)

If you mean the 555 timer IC (common exam topic):

• Modes: astable (free-running), monostable (one-shot), bistable (flip-flop-like)
• Astable frequency: f = 1.44 / ((RA + 2 RB) C) with RA and RB in ohms, C in farads
• Astable timings: Th = 0.693 (RA + RB) C (high), Tl = 0.693 RB C (low) → f ≈ 1.44 / ((RA + 2 RB) C)
• Monostable pulse width: t = 1.1 R C (R is the timing resistor, C is the timing capacitor)
• Threshold/trigger levels: 2/3 Vcc (threshold) and 1/3 Vcc (trigger)
• Typical circuits: LED flasher (astable), single-trigger pulse (monostable)

Which one would you like to focus on? If you want, I can solve a sample problem or go into a step-by-step derivation for the chosen topic.